Echo toggle/boolean options/settings

This is preliminary implementation. There are holes to be filled, and it
should probably be cleaned up some.
+ Only works for options which can be toggled; needs to be implemented
  for other option types
+ Doesn't handle window options, but once it does, there may be
  duplication between it and `RunSet`.
+ Does handle option abbreviations
+ Has some ugly nested matches
+ Definitely need to get Jared to review once I've matured it a bit