UI module exported functions:

	-- Initialize module. Register commands here.
	int ui_init ();

	-- Initialize arena. Argument is the arena structure with
	-- possible dimensions defined.
	int ui_initarena (ARENA *);

	-- Finish ui work... cleanup interface here.
	void ui_finish (void);

	-- Draw the arena. Called on each iteration
	void ui_drawarena (ARENA *);

	-- Draw a message.
	void ui_drawmessage (char *);

	-- Get a string from the user and return it
	char *ui_prompt (char *);

	-- Get an ascii character as pressed on the keyboard.
	-- This function is called until it return -1
	-- Buffering is considered ...
	int ui_getkey (void);