Make use of the multivalued property functions

lisp/gnorb-utils.el: (gnorb-trigger-todo-action) When getting/setting
the gnorb-message-msg-id-key property on entries, use
the *-multivalued-property convenience functions instead of replicating
them ourselves.
Provide more escapes for outgoing capture templates

lisp/gnorb-gnus.el: (gnorb-gnus-check-outgoing-headers
		    gnorb-gnus-sending-message-info,
		    gnorb-gnus-outgoing-make-todo-1)

		    Provide for the %:toname and %:toaddress escapes
		    when capturing TODOs from outgoing mails.
Guess which Org TODO is related to this message

lisp/gnorb-org.el: New function `gnorb-org-find-visit-candidates'. Used
		   when triggering a TODO state-change from a message:
		   now we make an intelligent guess as to which TODO
		   heading is wanted.

lisp/gnorb-gnus.el: Alter `gnorb-gnus-incoming-do-todo' to use the above
		    new function
Improve `gnorb-gnus-outgoing-make-todo'

lisp/gnorb-gnus.el: Now it does something intelligent when used on a
		    message that already belongs to a TODO email
		    conversation, as a reply.
FUNCTION RENAMING, I'M VERY SORRY

lisp/gnorb-gnus.el: Committing the cardinal sin of renaming user-facing
		    commands. My only excuse is that no one's probably
		    using this package yet.

		    gnorb-gnus-outgoing-make-todo is now
		    gnorb-gnus-outgoing-do-todo.

		    gnorb-gnus-message-trigger-todo is now
		    gnorb-gnus-incoming-do-todo.

		    gnorb-gnus-trigger-refile-args is now
		    gnorb-gnus-trigger-refile-targets.

		    Penance is being done, this won't happen again.
More complete docs: How to use Gnorb for email tracking

README.org: Various