Addresses ljvmiranda921#26.

The current implemenation maintains separate 2D board matrices
for each state to allow the use of existing lifeforms.

This board allows for the use of multistate automata.

Renames MultiStateBoard.states to state for consistency
with Board.

The fix ensures that, when adding lifeforms, each cell is in exactly
one state at a time i.e. only one of the entries in the state tensor
corresponding to that cell is set to True at any one time.

board.py now conforms with black style guide.

Fixed a bug with rps_life_rule with neighbour counting
caused by the array holding neighbour counts inheriting the
dtype bool from the state array.