change oid to id
change oid.hex
name as _oid
Fix tree commit.
Merge pull request #39 from xutao/ellen:fix

Fix tree commit.
Fix hook unlink.
Merge pull request #40 from xutao/ellen:fix

Fix hook unlink.
Merge pull request #37 from huanghuang/ellen:oid_id

change oid to id
Fix merge if no merge_base.
Merge pull request #41 from xutao/ellen:fix

Fix merge if no merge_base.
Catch OSError for fetch.
Merge pull request #42 from xutao/ellen:fix

Catch OSError for fetch.
Fix parents KeyError
Merge pull request #43 from xutao/ellen:fix

Fix parents KeyError