Add class method to check for valid reference names.
Implement objectByPeelingTagError: to peel a tag object.
Add objectByPeelingToType:error: to GTObject using git_object_peel.
Get the SHA from the unresolved target otherwise we'll crash later.
Add accessor for orphaned HEAD.
Clarify documentation on `isHeadDetached`.
Use `git_repository_head` instead of going through GTReference.

This is equivalent, but has a special error code for orphaned HEADs.
Change return type to id
Change < to !=
Change return type to id.
Change < to !=
Remove whitespace.
Add tests.
Merge pull request #214 from 5sw/tag_peel

Add wrappers for git_object_peel and git_tag_peel to GTObject/GTTag
Merge pull request #213 from 5sw/reference_is_valid

Add class method to check for valid reference names.
Merge branch 'master' into stuff
Add private `-lookupByGitOid:` to GTRepository.
Fix error code/domain when initing GTRepository with bad URL

Previous error used a code from kCFErrorDomainCFNetwork, but constructed
the error in NSCocoaErrorDomain.
Add method to initialize bare repositories

Also report an error if the passed URL is bad.
Add test for init bare repository