[RFC] Allow users to create Scala versions of any firrtl module

[chick]

Treadle could easily be extended to allow developers to write a Scala implementation of a chisel/firrtl module and override the simulation to use the software version instead of the hardware one. This could be a good way to incorporate golden model tests. This would be way of implementing aspect oriented programming in the unit test environment.

@edwardcwang please comment as you see fit.

[edwardcwang]

I think this makes sense. It's an extension of the current support for blackboxes right?