[reactive] Transforming Behaviors

[Greg Fitzgerald]

>> static transformations of dynamic geometry.
>> dynamic transformation of static geometry and dynamic transformation of
>> dynamic geometry.  And the corresponding three additional instances for 2D
>> geometry.  All six would be very useful.

Implementing just the dynamic transformation of dynamic geometry seems
to work out best.

instance Transform xf a => Transform (Behavior xf) (Behavior a) where
   (*%) = liftA2 (*%)

With the other instances, GHC complains about ambiguities, and it's
easy enough to pull either side up into the dynamic realm.

Thanks,
Greg