Reflog.xs: Added reflog support
16-reflog.t: Added reflog tests
Reflog.pm: Added reflog documentation
Remove reflog from TODO list
Changes: update
Raw.xs: rename GIT_NEW_OBJ() -> GIT_NEW_OBJ_WITH_MAGIC(), and add GIT_NEW_OBJ() (without magic)
Raw.xs: rename GIT_SV_TO_REPO() -> GIT_SV_TO_MAGIC()