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

- need_pack was not set to 0 when local fetch was already present causing  negotiate_fetch access violation

- added MSVC cmake definitions to disable warnings
- general.c is rewritten so it is ansi-c compatible and compiles ok on microsoft windows
- some MSVC reported warning fixes

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.

Improve error propagation in shallow call