git_buf_text_gather_stats doesn't work for multi-byte characters

Refresh readme and contributing guidance

Updating the contributing guidance to explain a bit more about how we use
PR's

Updated the methods of getting involved with the project and asking
questions.

Switch default calling convention to cdecl

git_revparse_ext: should return a NULL reference  when the revparse expression doesn't lead to a reference

don't include ignored as rename candidates

Small grammar fix in docs

Small fixes

Add `git_remote_owner`.

This reverts commit a91e4d6b.

Fixes return type documentation

Fix #1722

Plug some memory leaks

header files show up in vs and xcode

preload configuration paths

Update git__swap threading primitive

This makes git__swap use the __sync_lock_test_and_set primitive
with GCC and the InterlockedExchangePointer primitive with MSVC.
Previously is used compare_and_swap in a way that was probably
unintuitive for most thinking (i.e. it could fail to swap in the
value if another thread raced in).  Now it will always succeed
and the last thread to run in a race will win instead of the
first thread.

This also fixes up a little confusion between volatile void **
and void * volatile * that came up with the Win32 compiler.