Add transformers

This is not finished, but I wanted to make a PR so we could start discussing its implementation. This switches to using transformers for all of the compiling.

This are the issues that need to be closed before this will be ready:
- https://github.com/ForbesLindesay/transformers/issues/13
- https://github.com/ForbesLindesay/transformers/issues/12
- #153

And this will close:
- #97
- #92