Attempt #1 at enhancing the plugin

Provide an option which lets you mention what fields you don't want
emitted, and then remove them from the dicts to be published.

Not tested yet. Not even sure if it's correct.

TODOs:
- Line 111 needs to be checked. Do we check those values too?
- We could improve the option doc to include what fields one can mention
  there.


Possible fix for issue #3