This change adds the following new resource implementations: - RepositoryItemResource - RepositoryListResource - RepositoryBranchItemResource - RepositoryBranchListResource - RepositoryCommitItemResource - RepositoryCommitListResource - RepositoryGroupItemResource - RepositoryGroupListResource - RepositoryInfoResource - RepositoryUserItemResource - RepositoryUserListResource This involves one update to our base ListResource implementation (and various related plumbing) to allow subclasses to force a specific class type to be used for items. In the case of repository branches and commits, these are list resources that do not have an associated item endpoint or mimetype, and so the basic `_wrap_field()` and create functionality was returning a plain `ItemResource`. For this case, `ListResource` subclasses can now set `_item_resource_type` to force a specific item resource subclass instead. Testing Done: - Ran unit tests. - Used the new resources from a test script and saw that everything worked as expected.