Improved user input

Lots of reorganization to handling of user input.
	Perft n can now be called as a command.
	Moved parsing of user input to interaction.c
	Added convenience functions for switching between piece number and it's character symbol
Changed some loops to find individual piece positions by popping them off the bitboard instead of iterating over the pieces arraty.  This is in anticipation of removing the pieces array altogether at a later date.