Added a rank parameter when creating pieces. This should be the type of
piece being created (ie Rook, Queen, etc)
Created a == method for Positions, used when checking moves of pieces.
Created Rook Class, wrote generateValidMoves for rook class. Need to
test yet. Had to make it so piece has an instance of the board. I don't
like this, but I don't see a way around it.
Rook works as intended. Movement is restricted to only valid rook moves.