	Send a patch from the current or specified topic branch as
	email.

	Takes the patch given on the command line and emails it out.
	Destination addresses such as To, Cc and Bcc are taken from the
	patch header.

	Since it actually boils down to `git send-email` please refer to
	its documentation for details on how to setup email for git.
	You can pass arbitrary options to this command through the
	'-s' parameter, but you must double-quote everything.
	The '-r' parameter with msgid can be used to generate in-reply-to
	and reference headers to an earlier mail.

	TODO: 'tg mail patchfile' to mail an already exported patch
	TODO: mailing patch series
	TODO: specifying additional options and addresses on command
	      line

