object access API ================= Talk about <sha1_file.c> and <object.h> family, things like * read_sha1_file() * read_object_with_reference() * has_sha1_file() * write_sha1_file() * pretend_sha1_file() * lookup_{object,commit,tag,blob,tree} * parse_{object,commit,tag,blob,tree} * Use of object flags (JC, Shawn, Daniel, Dscho, Linus)