Added vmfactory functions to Connection.

* Their interfaces are now documented. They are of course not frozen
  yet, but hopefully I'll find that the interfaces are solid as I use
  them fully.
Wrote some documentation regarding Lua scripts.

* This is primarily to maintain consistency throughout the development
  of the Lua scripts. I'd usually put this sort of thing in the issue
  tracker but since the Lua scripts will be getting attentino for a
  long time more than likely, here seemed more appropriate.
Added documentation for core exceptions.

* This change makes it clear what happens if an error occurs in the
  backend (which can happen at any time because of network troubles or
  tons of other reasons).
Added vmfactory related core objects.

* These are all backend agnostic.