Added Check logic
Fixed valid_diagonal_move logic
Replace all occurences of 'ordinal' with 'cardinal'
Rename check to in_check, got it working
added dup method for board class
HOPEFULLY fixed valid_move? and in_check?
We think we have in_check working and all move logic, but not sure if things are broken because of added complexity
Added King move logic. All piece move logic should be working(?)
Added checkmate?, fixed diagonal move logic (change int division to float)
Added HumanPlayer class, get_move method
Added play loop, including some move error checking