Add testing with CTest and googletest
Simplify the doc target command
Add a test for get_winner in boardutil.h
Change the name of the testcase
Complete the winning conditions list
Change the hash_game_ended to get_winner

With has_game_ended you couldn't now who had won, because the player not
in turn could win by a wrong turn of the opponent. With get_winner you
know clearly who has won.
Document a bug