The name `git_transfer_progress` does not reflect its true purpose.

It suggests that it's progress for a non-existence `git_transfer`
object, and is used for indexing callbacks more broadly than just
during transfers.

Rename `git_transfer_progress` to `git_indexer_progress`.

High-level map APIs

refdb_fs: fix loose/packed refs lookup racing with repacks

Allocator restructuring

cache: fix misnaming of `git_cache_free`

examples: produce single cgit2 binary

Functions that free a structure's contents but not the structure
itself shall be named `dispose` in the libgit2 project, but the
function `git_cache_free` does not follow this naming pattern.

Fix this by renaming it to `git_cache_dispose` and adjusting all
callers to make use of the new name.

In commit 6e0dfc6f (Make stdalloc__reallocarray call
stdalloc__realloc, 2019-02-16), we have changed the stdalloc
allocator to reuse `stdalloc__realloc` to implement
`stdalloc__reallocarray`. This commit is making the same change
for the Windows-specific crtdbg allocator to avoid code
duplication.

The Windows-specific crtdbg allocator is currently mixed into the
crtdbg stacktracing compilation unit, making it harder to find
than necessary. Extract it and move it into the new "allocators/"
subdirectory to improve discoverability.

This change means that the crtdbg compilation unit is now
compiled unconditionally, whereas it has previously only been
compiled on Windows platforms. Thus we now have additional guards
around the code so that it will only be compiled if
GIT_MSVC_CRTDBG is defined. This also allows us to move over the
fallback-implementation of `git_win32_crtdbg_init_allocator` into
the same compilation unit.

Right now, our two allocator implementations are scattered around
the tree in "stdalloc.h" and "win32/w32_crtdbg_stacktrace.h".
Start grouping them together in a single directory "allocators/",
similar to how e.g. our streams are organized.

Remove public 'inttypes.h' header

Remove an `inttypes.h` header that is too large in scope, and far too
public.

For Visual Studio 2012 and earlier (ie, `_MSC_VER < 1800`), we do need
to include `stdint.h` in our public headers, for types like `uint32_t`.

Internally, we also need to define `PRId64` as a printf formatting
string when it is not available.

Prevent reading out of bounds memory

Previously, we would fail to correctly truncate the source buffer
if the source has more than one line and ends with a non-newline
character. In the following call, we thus truncate the source
string in the middle of the second line. Without the bug fixed,
we would successfully apply the patch to the source and return
success. With the overflow being fixed, we should return an
error now.

When parsing the patch image from a string, we split the string
by newlines to get a line-based view of it. To split, we use
`memchr` on the buffer and limit the buffer length by the
original length provided by the caller. This works just fine for
the first line, but for every subsequent line we need to actually
subtract the amount of bytes that we have already read.

The above issue can be easily triggered by having a source buffer
with at least two lines, where the second line does _not_ end in
a newline. Given a string "foo\nb", we have an original length of
five bytes. After having extracted the first line, we will point
to 'b' and again try to `memchr(p, '\n', 5)`, resulting in an
out-of-bounds read of four bytes.

Fix the issue by correctly subtracting the amount of bytes
already read.

Fix a memory leak in odb_otype_fast()

This change frees a copy of a cached object in odb_otype_fast().

Make stdalloc__reallocarray call stdalloc__realloc

Remove `git_time_monotonic`

Fix a _very_ improbable memory leak in git_odb_new()

`git_time_monotonic` was added so that non-native bindings like rugged
could get high-resolution timing for benchmarking.  However, this is
outside the scope of libgit2 *and* rugged decided not to use this
function in the first place.

Google suggests that absolutely _nobody_ is using this function and we
don't want to be in the benchmarking business.  Remove the function.

ci: publish documentation on merge

When a commit is pushed or merged into one of the release branches
(master, maint/*) then push the documentation update to gh-pages.

This reverts commit 2a4e866a.

When a continuous integration build runs (ie a commit is pushed or
merged into one of the CI branches, `master` or `maint/*`) then push the
rebuilt documentation into the `gh-pages` branch.

This change fixes a mostly theoretical memory leak in got_odb_new()
that can only manifest if git_cache_init() fails due to running out of
memory or not being able to acquire its lock.

This change avoids calling realloc(3) in more than one place.

Remove the low-level interface that was exposing implementation details of
`git_idxmap` to callers. From now on, only the high-level functions shall be
used to retrieve or modify values of a map. Adjust remaining existing callers.

Remove the low-level interface that was exposing implementation details of
`git_oidmap` to callers. From now on, only the high-level functions shall be
used to retrieve or modify values of a map. Adjust remaining existing callers.

Remove the low-level interface that was exposing implementation details of
`git_offmap` to callers. From now on, only the high-level functions shall be
used to retrieve or modify values of a map. Adjust remaining existing callers.

Remove the low-level interface that was exposing implementation details of
`git_strmap` to callers. From now on, only the high-level functions shall be
used to retrieve or modify values of a map. Adjust remaining existing callers.

To relieve us from memory pressure, we may regularly call `cache_evict_entries`
to remove some entries from it. Unfortunately, our cache does not support a
least-recently-used mode or something similar, which is why we evict entries
completeley at random right now. Thing is, this is only possible due to the map
interfaces exposing the entry indices, and we intend to completely remove those
to decouple map users from map implementations. As soon as that is done, we are
unable to do this random eviction anymore.

Convert this to make use of an iterator for now. Obviously, there is no random
eviction possible like that anymore, but we'll always start by evicting from the
beginning of the map. Due to hashing, one may hope that the selected buckets
will be evicted at least in some way unpredictably. But more likely than not,
this will not be the case. But let's see what happens and if any users complain
about degraded performance. If so, we might come up with a different scheme than
random removal, e.g. by using an LRU cache.

To compute whether there are objects missing in a packfile, the indexer keeps
around a map of OIDs that it still expects to see. This map does not store any
values at all, but in fact the keys are owned by the map itself. Right now, we
free these keys by iterating over the map and freeing the key itself, which is
kind of awkward as keys are expected to be constant.

We can make this a bit prettier by inserting the OID as value, too. As we
already store the `NULL` pointer either way, this does not increase memory
usage, but makes the code a tad more clear. Furthermore, we convert the
previously existing map iteration via indices to make use of an iterator,
instead.

Currently, our headers need to leak some implementation details of maps due to
their direct use of indices in the implementation of their foreach macros. This
makes it impossible to completely hide the map structures away, and also makes
it impossible to include the khash implementation header in the C files of the
respective map only.

This is now being fixed by providing a high-level iteration interface
`map_iterate`, which takes as inputs the map that shall be iterated over, an
iterator as well as the locations where keys and values shall be put into. For
simplicity's sake, the iterator is a simple `size_t` that shall initialized to
`0` on the first call. All existing foreach macros are then adjusted to make use
of this new function.

Some callers were still using the tightly-coupled pattern of `lookup_index` and
`valid_index` to verify that an entry exists in a map. Instead, use the more
high-level `exists` functions to decouple map users from its implementation.

Currently, the delete functions of maps do not provide a return value. Like
this, it is impossible to tell whether the entry has really been deleted or not.
Change the implementation to provide either a return value of zero if the entry
has been successfully deleted or `GIT_ENOTFOUND` if the key could not be found.

Convert callers to the `delete_at` functions to instead use this higher-level
interface.

The currently existing function `git_idxmap_resize` and
`git_idxmap_icase_resize` do not return any error codes at all due to their
previous implementation making use of a macro. Due to that, it is impossible to
see whether the resize operation might have failed due to an out-of-memory
situation.

Fix this by providing a proper error code. Adjust callers to make use of it.

Currently, one would use the function `git_idxmap_insert` to insert key/value
pairs into a map. This function has historically been a macro, which is why its
syntax is kind of weird: instead of returning an error code directly, it instead
has to be passed a pointer to where the return value shall be stored. This does
not match libgit2's common idiom of directly returning error codes.

Introduce a new function `git_idxmap_set`, which takes as parameters the map,
key and value and directly returns an error code. Convert all callers of
`git_idxmap_insert` to make use of it.