Major refactoring...

Collapsed Pieces class into Suspects class.  Now the Weapons, Rooms and
Suspects classes are each modeling the piece and the card in the game.
Also I re-factored @picked on Suspects to be a class variable - just
didn't make sense as an instance variable because there could only be
one instance of Suspects or picked? method logic would fail.  Then had
to change attr_reader :list to a class method since attr_reader only
works for instance attributes.