Add empty transformation plugin implementation
Eliminate nosetests star import
Tweak noop plugin implemenation
Add failing test for plugins
Run plugins after build_document_set
Implement run_plugins
Add link in readme to backdrop-collector-plugins
Further enhance plugins documentation
Merge pull request #40 from pwaller/plugin

Add plugin architecture
Log at level INFO rather than DEBUG

Production logs are incredibly noisy with useless logs. This should
ultimately be handled by an environment variable.
Merge pull request #42 from alphagov/info-logging

Log at level INFO rather than DEBUG