Fix sharedmethod to not cache created classmethods and instancemethods.  In retrospect it should have been blatantly obvious that was a bad idea, and unnecessary anyways.  Turns out Python creates a new method object every time you access a method on an object anyways (this is still reasonably efficient, as it uses a cache of already malloc'd PyMethodObjects and just updates the im_func and im_self pointers on those objects).
A better default docstring for __call__ -- this can still be greatly improved, later.
Fix basic composition of models with different numbers of outputs
Allow a name to be specified on compound model instances
Don't repr ExpressionTrees as an ascii tree for now, at least not until the enhancements to the tree display are complete.