A few fixes have accumulated in this area which have made the freeing of
data a bit muddy. Make sure to free the data only when needed and once.

When we are going to write a delta to the packfile, we need to free the
data, otherwise leave it. The current version of the code mixes up the
checks for po->data and po->delta_data.

Fix the description for `GIT_FEATURE_SSH`.

caps: Rename to features to avoid confusion

Do not allow git_branch_create() to force update branch

Add project list and update readme

Add git_diff_buffers and git_patch_from_buffers

This adds `git_diff_buffers` and `git_patch_from_buffers`.  This
also includes a bunch of internal refactoring to increase the
shared code between these functions and the blob-to-blob and
blob-to-buffer APIs, as well as some higher level assert helpers
in the tests to also remove redundancy.

Blame first-parent history

Remove "ignore" state from the git.git-authors

Also, correct test case to account for the boundary flag

Move system directory cache out of utils

Include stdarg.h for the va_copy test

Fix Intel compiler warnings

Improve documentation for merging

Check if librt exists independent of OS, to be able to exclude librt on ...

Improve C89 compatibility and clarify use of C99 features

Check if librt exists independent of OS, to be able to exclude librt on Android builds, even though it is a 'Linux'.

* Make GIT_INLINE an internal definition so it cannot be used in
  public headers
* Fix language in CONTRIBUTING
* Make index caps API use signed instead of unsigned values

and a couple of other minor doc fixups.