Fixed bitboard_position()
Added more error codes and updated the todo list
Mostly implemented player_take_turn and player_validate_input
These functions still need finishing off. See the todo list for more info.
 On branch master
 Changes to be committed:
	modified:   player.c
	modified:   player.h
 Changes not staged for commit:
	modified:   main.c
Added error condition for when an invalid move is made