Taking a stab at bulk testing importers.

I used the code from `testing.py` as inspiration but tried to match the
approach used in `_extract`

This adds a commands to the cli for `test` and `generate` that can use
the same importer configurations as you would use for typical use.

I dont know that this is necessarily a good approach and would love
feedback on how I could improve this or alternate paths for making
testing custom beangulp importers easier.

Author: alexrkaufman