Fix the smart HTTP protocol

• Fix support for the smart HTTP protocol (report by @talex5, mirage/irmin#138)

Remove `OGITTMPDIR`

• Remove the OGITTMPDIR and alway store temp files under git/tmp (mirage/irmin#132)

Fix bug in LRU cache, flush the `cat-file` commands

• Fix LRU cache: SHA1 should be unique in the cache (regression
  introduced in 1.4.3). This was causing confusing read results
  under load.
• Reading objects now updates the LRU cache
• Fix a regression in ogit cat-file which were displaying nothing
  for small objects.

Fix for non-bare repositories, remove stdout/stderr messages

• Fix the filesystem updates for non-bare repositories (reported by @avsm)
• Git.write_index now takes an optional index argument
• Index entries should be fixed alphabetically
• Remove raw printf (#60)
• More flexibility on where to write temp files. The directory name can be
  configured by write calls, and the default is OGITTMPDIR if set,
  then Filename.get_temp_dir_name -- as it was in 1.4.5, see #51

Improve LRU settings and add the `git.top` package

• Expose Git.Value.Cache.set_size to change the LRU cache size
• Reduce the default LRU cache size (in 1.4.4 it was set to 64k, now it's 512)
• More precise type for commit dates
• Add git.top to load toplevel printers for Git values

Support packed references

• Support packed-refs files, to read references packed by git gc (reported
  by Gregory Tsipenyuk)
• Fix the filesystem backend when TMPDIR is not on the same partition as the
  Git repository (#51, patch from @vklquevs)

More protocol support, more stability

• Support the smart HTTP Git protocol (#26)
• Best-effort creation of files when expanding the index into the filesystem:
  Skip the invalid filenames and continue. Users are expected to sanitize
  their filenames if they want to use a non-bare repository (#11)
• Overwrite changed file when expanding the index into the filesystem (#4)
• Do not recompute the hash of blob files when expanding the index into the
  filesystem. This help fixing a speed issue with non-bare repo with lots of
  file.
• Rename {write,read}_cache to {write,read}_index
• Rename Cache to Index
• Expose the protocol capabilities to the client
• Support side-band-64k protocol capability (#44)
• Fix support for git+ssh (#39)
• Expose zlib compression level (#41)
• Maintain a cache of opened files (#29, Pierre Chambart)

Fix caching and concurrent operations

• Fix regression introduced in 1.4.3 appearing when
  synchronising big repositories (#38)
• Fix concurrent read/write by using an atomic rename (#35)
• Tree objects can also point to commits (@codinuum)
• Reduce allocation (@codinuum)
• Use LRU cache instead of an unbounde Hashtl
  (code imported for Simon Cruanes's CCache implementation)
• Remove the crazy unbounded caching in Git.FS. Use the LRU
  everywhere (#22)
• Fix fd leaking (#29)
• Update to dolog.1.0
• Remove dependency to camlp4
• Remove lots of warnings
• Move Git_unix and Git_mirage in their own subdirs as it
  was causing issues to oasis (#5, Simon Cruanes)
• Use Bytes instead of String (#5, Simon Cruanes)

Fix writing of empty files

• Fix Git_unix.IO.write_file to work on empty files

Fix `ogit --version` and expose more values

• Fix ogit --version (#22)
• Expose the backend type
• Expose Git_unix.Sync.IO