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.

doc/Guidebook.mn

@@ -4529,6 +4529,9 @@ screen.
 uses a timer-based delay.
 The default is on if configured into the program.)
 Persistent.
+.lp "tips    "
+Show some helpful tips during gameplay (default on).
+Persistent.
 .lp tombstone
 Draw a tombstone graphic upon your death (default on).
 Persistent.