Fix state when HEAD is not detached

Let the user grab the packfile as it's being written

Fix bytes_received in fetch tests - we weren't calling the callback

Initial implementation of diff rename detection

Free conflict index entries on removal

Prefer GetLastError() for GITERR_OS on Win32

Improve docs, examples, warnings

Some more changes to the Index API

This improves docs in some of the public header files, cleans
up and improves some of the example code, and fixes a couple
of pedantic warnings in places.

Why Apple, why?

Update of text stats calculation

Do not interpret 0x85 as Next Line (NEL)
char when gathering statistics for a text file.

Reorganize transport architecture

Let the user get each object as a buffer+size pair so they can handle
the packfile content as they need to.

This adds a new API that allows users to reload the config if the
file has changed on disk.  A new config callback function to
refresh the config was added.

The modified time and file size are used to test if the file needs
to be reloaded (and are now stored in the disk backend object).

In writing tests, just using mtime was a problem / race, so I
wanted to check file size as well.  To support that, I extended
`git_futils_readbuffer_updated` to optionally check file size in
addition to mtime, and I added a new function `git_filebuf_stats`
to fetch the mtime and size for an open filebuf (so that the
config could be easily refreshed after a write).

Lastly, I moved some similar file checking code for attributes
into filebuf.  It is still only being used for attrs, but it
seems potentially reusable, so I thought I'd move it over.

Add git_diff_patch_to_str API

repo: enhance git_repository_state() detection

Index changes