Add method to create a new lightweight tag.
Merge remote-tracking branch 'refs/remotes/upstream/master' into lightweight_tag

Conflicts:
	Classes/GTTag.h
Move methods to create new tags to GTRepository and call them from the GTTag class methods.
Remove class methods to create new tags from GTTag and update unit tests.
Whitespace fixes.
Fix doc indentation.
Move test cases from GTTagTest to GTRepositorySpec and move to expect() syntax.
Merge branch 'master' into lightweight_tag

Conflicts:
	Classes/GTTag.m
	ObjectiveGitTests/GTTagTest.m
Use uppercase SHA and OID names
Fix style issues.
Merge branch 'refs/heads/master' into lightweight_tag
Merge pull request #212 from 5sw/lightweight_tag

Add method to create a new lightweight tag.