Git format and protocol in pure OCaml

Support for on-disk and in-memory Git stores. Can read and write all the Git objects: the usual blobs, trees, commits and tags but also the pack files, pack indexes and the index file (where the staging area lives).

All the objects share a consistent API, and convenience functions are provided to manipulate the different objects. For instance, it is possible to make a pack file position independent (as the Zlib compression might change the relative offsets between the packed objects), to generate pack indexes from pack files, or to expand the filesystem of a given commit.