Merge pull request #2 from carlosmn/signature

Introduce Signature
Free Git objects via finalizers or manually

Provide a manual way of freeing objects, but set finalizers for them
in case the user does not want to worry about memory management, which
would be useful for commits or trees, which sare typically small.

When the objects are freed manually, the finalizer is unset to avoid
double-freeing, mimicking what the go runtime does.
Merge pull request #3 from carlosmn/finalizers

Free Git objects via finalizers or manually
Wrap git_index
Test the index code slightly
Merge pull request #4 from carlosmn/index

Wrap the index and test it a bit
Repository.CreateCommit
Update README
Properly wrap ODB objects
Repository.Path
Sane names yo
Fixed renamed func in index_test
Merge pull request #5 from mrb/test_fix

Fixed renamed func in index_test
Use time.Time in the Signature struct