pack-objects: free memory safely

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.

Remove ignored files from the working directory if they were stashed

Added a test, that fails for #2133

BUGFIX - Fetching twice from the same remote causes a segfault

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

- 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