More pseudofunctors (but not as many as I'd like)

Define the identity pseudofunctor, and pseudofunctors from initial and terminal categories.

I'd love help figuring out why it takes 13 seconds on my machine (so, probably 30 seconds on travis) to define the identity pseudofunctor.

I had another commit which reorganized the rewriting laws for pseudofunctors a bit.  Unfortunately, it added 45 seconds on my machine, and caused a 50% slowdown in the Grothendieck construction of a pseudofunctor to Cat.  So I'm going to hold on to that one until I figure out what's going on.