Expose relay control commands.
Avoid using lambdas in the power on/off macro definitions, to start making them a bit more portable.
Use method-based access, not an internal reference to the device, in the power macros.
Rewrite lots of Event-handling code to be Pyro-friendly; the power-on macro is now defined client-side, not controller-side.
Client-side macro for system power off, too.
Fix test to assert the new client-side macro behaviour.
All of which means these methods are no longer used. Closes issue #40.
Tidy of sequencer code.
Tidy up doc.