Debugging the files.

There is a memory error some where, attempting to track it down.
Modified checker_board.hpp and game_piece.hpp.

Fixed the memory bug, it was a missing return statement in the
Game_Piece class function get_moves.

Decided that the map should be switched over to coordinates to help with
not having to translate from pairs to strings and vice versa. Thus, a
number of functions just needed a parameter change.
Modified .gitignore file.

Added in an Git exception for the build directory.
Merge branch 'debug' into checker-board

Merging the memory fix from debug back in to the checker-board branch.