Changed internal board representation
- Added a bunch of constants to represent areas of the board etc
- Each gameboard struct now only stores the positions of black pieces, white pieces
  and if a square is a king
- Fixed gameboard_print so that it works with the new representation.
- Added a basic test function to main.c for messing around with.
 On branch master
 Changes to be committed:
	modified:   bitboard.c
	modified:   bitboard.h
	modified:   main.c