Tips and option to disable them

Adds a more general way to handle gameplay tips, and adds
a boolean option "tips", which can be used to disable all
tips.  Adds a helpful longer message when the game goes
into the "farlook" mode.

Also adds a lua binding to easily show multi-line text
in a menu window.

Breaks save compat.

include/hack.h

@@ -519,6 +519,7 @@ enum nhcore_calls {
     NHCORE_RESTORE_OLD_GAME,
     NHCORE_MOVELOOP_TURN,
     NHCORE_GAME_EXIT,
+    NHCORE_GETPOS_TIP,
 
     NUM_NHCORE_CALLS
 };