Minor bug fixes, started on player.py

Merged branches 'applicative' and 'applicative-remodulate'. ...

The basic structure of the ATL interpreter now stands and (sort of)
works, still some bugs though. And obviously plenty of features left
to add (currently implemented: define-place, description, neighbours).

Ready to merge back into master.

Wrote most of the interpreter, need to find bugs now to get it to work.

Significant progress, especially in place.py and parser.py

Wrote example.atl, the reference file for the Atlantis language. ...

Started on main code.