Dispatcher refactory.

We now have a public Dispatcher interface which is where one now finds curFn
and prevFn (much nicer than having those in RBufferView), and which one can use
to complete and invoke fns by name. Any other fn fun will also live therein.

execute-extended-command is now wired up, though without tab completion, it's
very unpleasant to use. That's up next!
Minibuffer tab completion. Woo!

I still need to wire up the popup when you have more than one valid completion,
but my fingers are already feeling good about this.
Added goto-line.

Yay for working minibuffer reads.
Wired up ESC handling.

ESC causes the next key press to be meta-fied.