Add the function #vow-promotion-position.
Fix minor error: change fn reference to #to-white.
Add function #promotion-position-from.
Add fns #occupied? and #promotion-position-set?.
Add public fn #promote as well as helper fn #copy;
modify fn #game-completed-response so that it returns a valid 'context' object.
Modify a helper function in the specs for
#query-game-service so that the helper function returns a response with
a valid promotionPosition.
Add a file that defines a user interface and a main file
that initializes the user interface.