Missing documentation for signatures

[miselico]

The State and Deck class use a system of signatures to indicate which player can access what.
How these are used exactly is not documented anywhere and it appears some accesses are still possible.

2 solutions:

1. Figure out and document how they work, document and fix the places where the access contract is broken
2. Create a decorator for the state that hides away what a player should not see/know.