add REPL for method calls before UI for secondary features is entirely designed/refined

This is a fairly lightweight patchset that lets you enter a command like "session.devices[0].ctrl_transfer(0x51, 0, 0)" under the documentation pane, which is evaluated and (in this particular instance) calls the control request with proper parameters to turn PIO0 high.

Reference https://github.com/itdaniher/ubuild/blob/master/IO.mkd for other not-quite-yet-supported functionality.