write proper docs (asciidoc format for git compatibility)

	delete tempdir

	'git subtree rejoin' option to do the same as --rejoin, eg. after a
	  rebase

	--prefix doesn't force the subtree correctly in merge/pull:
	"-s subtree" should be given an explicit subtree option?
		There doesn't seem to be a way to do this.  We'd have to
		patch git-merge-subtree.  Ugh.

	add a 'push' subcommand to parallel 'pull'
	
	add a 'log' subcommand to see what's new in a subtree?

	add a --squash option so we don't merge histories but can still split
	
	add to-submodule and from-submodule commands