Explicitly truncate the file size to a `uint32_t`.

Don't calculate 4 GiB as that will produce a compiler warning on MSVC.
Just hardcode it.

errors: use lowercase

largefile tests: only write 2GB on 32-bit platforms

Use lowercase for our error messages, per our custom.

Don't try to feed 4 GB of data to APIs that only take a `size_t` on
32-bit platforms.

Fix broken link in README

net: remove unused `git_headlist_cb`

cmake: default NTLM client to off if no HTTPS support

If building libgit2 with `-DUSE_HTTPS=NO`, then CMake will
generate an error complaining that there's no usable HTTPS
backend for NTLM. In fact, it doesn't make sense to support NTLM
when we don't support HTTPS. So let's should just have
NTLM default to OFF when HTTPS is disabled to make life easier
and to fix our OSSFuzz builds failing.

attr: rename constants and macros for consistency

Our enumeration values are not generally suffixed with `T`.  Further,
our enumeration names are generally more descriptive.

Change API instances of `fromnoun` to `from_noun` (with an underscore)

object: rename git_object__size to git_object_size

The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the tag function for
consistency with the rest of the library.

The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the index functions for
consistency with the rest of the library.

We don't use double-underscores in the public API.

The majority of functions are named `from_something` (with an
underscore) instead of `fromsomething`.  Update the blob functions for
consistency with the rest of the library.

The only function that is named `issomething` (without underscore) was
`git_oid_iszero`.  Rename it to `git_oid_is_zero` for consistency with
the rest of the library.

Replace fnmatch with wildmatch

Documentation fixes

Docurium seems to choke on this header because it can't see both
git_indexer_progress & git_indexer_progress_cb, let's add the include.

The `fnmatch` code has now been completely replaced by
`wildmatch`, same as upstream git.git has been doing in 2014.
Remove it.

Upstream git has converted to use `wildmatch` instead of
`fnmatch`. Convert our gitattributes logic to use `wildmatch` as
the last user of `fnmatch`. Please, don't expect I know what I'm
doing here: the fnmatch parser is one of the most fun things to
play around with as it has a sh*tload of weird cases. In all
honesty, I'm simply relying on our tests that are by now rather
comprehensive in that area.

The conversion actually fixes compatibility with how git.git
parser "**" patterns when the given path does not contain any
directory separators. Previously, a pattern "**.foo" erroneously
wouldn't match a file "x.foo", while git.git would match.

Remove the new-unused LEADINGDIR/NOLEADINGDIR flags for
`git_attr_fnmatch`.