fix github pull request #355 - Sokoban cheating

Track sokoban cheating (taking actions that incur a luck penalty).
The pull request only reported the number of times (possibly zero)
that the player broke nethack's sokoban rules when reporting the
"you obtained the Sokoban prize" achievement, which is when the
count is most meaningful, but this implements it as a full-fledged
conduct instead.  This way the #conduct command can be used after
"creative nethacking" to check immediately whether an action has
violated the Sokoban rules so a player willing to put in a bit of
effort can eventually learn which actions have a negative impact.

The new conduct is only shown during games where the character has
entered the Sokoban branch, but once that has happened it gets shown
no matter the location at the time of #conduct or end of game.

Most of this wasn't in the pull request:  expanding the Guidebook to
give more information about sokoban and its conduct.

Bump EDITLEVEL to invalidate to-be-3.7 save files because u.uconduct
has been extended.

Fixes #355

include/patchlevel.h

@@ -1,4 +1,4 @@
-/* NetHack 3.7	patchlevel.h	$NHDT-Date: 1581322658 2020/02/10 08:17:38 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.156 $ */
+/* NetHack 3.7	patchlevel.h	$NHDT-Date: 1593768081 2020/07/03 09:21:21 $  $NHDT-Branch: NetHack-3.7 $:$NHDT-Revision: 1.165 $ */
 /* Copyright (c) Stichting Mathematisch Centrum, Amsterdam, 1985. */
 /*-Copyright (c) Michael Allison, 2012. */
 /* NetHack may be freely redistributed.  See license for details. */
@@ -14,7 +14,7 @@
  * Incrementing EDITLEVEL can be used to force invalidation of old bones
  * and save files.
  */
-#define EDITLEVEL 20
+#define EDITLEVEL 21
 
 #define COPYRIGHT_BANNER_A "NetHack, Copyright 1985-2020"
 #define COPYRIGHT_BANNER_B \