All the tests pass \o/
Style improvement, API cleanups, improved speed

- All the tests pass
- 'ogit git://github.com/ocaml/opam-repository' works both
  with and without --unpack, using a reasonable amount of
  time (half the time is used to download the pack file:
  would be nice to process it in a streaming way later).
- Still a minor problem in the index pack generation from
  a received pack file. Git complains about the index being
  too short. Looking at that now.

ogit clone git://github.