`oid_strlen` has meant one more than the length of the string.
This is mighty confusing.  Make it mean only the string length!
Whomsoever needs to allocate a buffer to hold a string can null
terminate it like normal.

Handle prefixes (in terms of number of path components) for patch
parsing.

When a text file is added or deleted, use the file names from the
`diff --git` header instead of the `---` or `+++` lines.  This is
for compatibility with git.

We may have parsed binary data, set the `SHOW_BINARY` flag which
indicates that we have actually computed a binary diff.

Now that `git_diff_delta` data can be produced by reading patch
file data, which may have an abbreviated oid, allow consumers to
know that the id is abbreviated.

No need to replicate the old_file/new_file members, or plumb them
strangely up.

Patches can now come from a variety of sources - either internally
generated (from diffing two commits) or as the results of parsing
some external data.

When we are provided some input buffer (with a length) to inflate,
and it contains more data than simply the deflated data, fail.
zlib will helpfully tell us when it is done reading (via Z_STREAM_END),
so if there is data leftover in the input buffer, fail lest we
continually try to inflate it.

Handle the application of binary patches.  Include tests that
produce a binary patch (an in-memory `git_patch` object),
then enusre that the patch applies correctly.

Introduce `git_zstream_inflatebuf` for simple uses.

Refactor the git_delta functions to have consistent naming and
parameters with the rest of the library.

Move the delta application functions into `delta.c`, next to the
similar delta creation functions.  Make the `git__delta_apply`
functions adhere to other naming and parameter style within the
library.

When a patch is empty, simply copy the source into the destination.

The beginnings of patch application from an existing (diff-created)
git_patch object: applies the hunks of a git_patch to a buffer.

Use AppVeyor's Start-FileDownload cmdlet

test: Fix stat() test to mask out unwanted bits

Don't generate conflicts when checking out a modified submodule and the
submodule is dirty or modified in the workdir.

Fix comment for GIT_FILEMODE_LINK

Start-FileDownload maintains current directory context and allows
specifying a request timeout, see [1].

[1] https://www.appveyor.com/docs/how-to/download-file#start-filedownload-cmdlet

Haiku and Hurd both pass extra bits in struct stat::st_mode.

tree: handle removal of all entries in the updater