Branch of main project with `theano` commented out

[ColCarroll]

I tried to do this mostly agnostically, but added a few pieces of pytorch code...

This commit should keep pointing to a project where import pymc3 works without theano. The import statements are commented out, but interior code that was changed was marked with

# THEANO  whatever = tt.original_code()
whatever = None

so that it is greppable.

Let me know if it would be helpful for me to drop that version of the project into one of the subfolders!

[twiecki]

Definitely put it into a folder here.