show the diff of files between two commits

EXAMPLES
	git diff
		show the diff between the working copy and HEAD (i.e. see what you're about to stage)
	git diff --staged
		show the diff between the staging area and HEAD (i.e. see what you're about to commit)
	git diff master
		show the diff between HEAD and master
	git diff commit-hash1 commit-hash2
		show the diff between two commits identified by their hashes
	git diff branch1 branch2
		show the diff between the latest commits in branch1 and branch2

FLAGS
	--staged	diff between the staging area and some commit (default: HEAD)
