Fixed row and column of _pgn_move_to_coords being switched. Tests are still passing. Began writing tests for _is_check. Modified _is_check to stop using king evaluator (causes infinite recursion).
Added tests for _is_check.
Implemented tests for _is_checkmate. Tweaked _is_checkmate to pass tests.
Implemented _board_to_image_string and its tests. Tests are passing.
Initial API implementation.
Fixed ability of chessnut object to print the correct PGN game string representing the game state.