Groupings are now read and written to XML.
Merge branch 'groupings'

Conflicts:
	backend/xml.py

Representation for groupings plus the ability to export to/import from XML
was added in the `groupings' branch. User interface is not ready yet.
Finalized the merge.

Removed generated and data files, restored task.py.
Merge branch 'master' into python3.1

Conflicts:
	task.py
	wyrdin.py

This branch now contains all the newest code written, and should
additionally be runnable from within Python 3.1. By the way, I changed the
configuration to using XML again, in order to have a functioning program.
(Else, it would complain about not implementing `read_groups' for pickling,
which is right.)
Finalised merge with master (again?).
Answered Richard's questions.