Moved the transform code from prov2ce into provglish.transform.Transform

This means it will be possible to test. The tests have yet to be written.
Created transform.Transform.transform

This function takes a graph and returns the minimal sentence set.
Removed the ce.CE class.

Instead, all of its members are just loaded into the root of the module.

This should make the code look prettier.
A big update, moving stuff around.

This means that all the functionality should now appear in the right places, making
the API a lot more useable.