Merge branch 'jc/doc-diff-blobs'

"git diff <blob> <blob>" was not documented and was only hinted as an extension to "git diff <commit> <commit> -- <pathspec>", but comparison between two blobs are more special than that. It does not take any pathspec to begin with. * jc/doc-diff-blobs: Documentation: Describe "git diff <blob> <blob>" separately