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.

dat/opthelp

@@ -66,6 +66,7 @@ sparkle        display sparkly effect for resisted magical         [True]
 standout       use standout mode for --More-- on messages         [False]
 status_updates update the status lines                             [True]
 time           display elapsed game time, in moves                [False]
+tips           show some helpful tips during gameplay              [True]
 tombstone      print tombstone when you die                        [True]
 toptenwin      print topten in a window rather than stdout        [False]
 travel         enables travelling via mouse click if supported;    [True]