added stash command
better formatting
Merge branch 'master' into mmm_stash

Conflicts:
	Classes/GTRepository.h
Fix issues raised in review.
Add stash drop & enumeration support.
Review.
Merge branch 'tree-contents' into mmm_stash

The stash tests need access to the contents of the stashed commit.
Test stashes with empty workdir.
Merge remote-tracking branch 'origin/master' into stash

Conflicts:
	Classes/GTRepository.h
	Classes/GTRepository.m
Minor style fixes, check for nil messages
Minor doc tweaks
More stashing tests
Bump to libgit2/libgit2#1881
++libgit2
Break stashing methods out into a category
Use -lookupObjectByGitOid:
Document the ordering of stash indices
Test/fix stash enumeration
Merge pull request #265 from libgit2/stash

Stash support