Fixed a checkmate bug being caused by using a != instead of an 'is not'.
Added logic to _is_checkmate that allows for using a friendly piece to block the threat (which wasn't possible beore). This logic is not yet tested.
Implemented test for new checkmating logic. Test appears to be passing.
Added king-position-tracking logic to castling evaluators.
Added tests to insure that moving kings and rooks disallows castling in the future. Refactored so that tests pass.
Added tests ensuring that kings are properly tracked when castling.
Added tests asserting that a checkmate sets the is_over and winner attributes of the game. Refactored so that tests pass.
Implemented tests to assert that king position is being tracked. Tests are passing.
Fixed styling.