Add effect typing

[girving]

The syntax should probably be something like

print "blah" :: E e ()

where E means "effect", e is the particular effect(s), and () is the result type of the evaluation. However we implement it, the space of effect annotations e should be a complete lattice. In particular, we want the ability to write something like "E None t" which is identical to t or "E Any t" which can have any effect (useful for wrapping weird C functions).

[dylex]

This was enlightening and possibly useful: http://www.cs.ucla.edu/~todd/research/tldi09.html
It seems like we might need a way to declare new effects, and that we need some way to specify effect sets, possibly by a definable hierarchy (ala type classes).