add #genocided command

Comparable to #vanquished, be able to view info normally available
during end of game disclosure while the game is still in progress.
The new #genocided command lists all genocided and extincted types
of monsters.  Unlike #vanquished, there aren't any sorting choices.

Potential future enhancement:  provide a way to view the genocided
list at the "what do you want to genocide?" prompt.

doc/Guidebook.mn

@@ -1298,6 +1298,10 @@ Default key is \(oqf\(cq.
 Force a lock.
 Autocompletes.
 Default key is \(oqM-f\(cq.
+.lp #genocided
+List any monster types which have been genocided or become extinct.
+Autocompletes.
+Default key is \(oqM-g\(cq.
 .lp "#glance  "
 Show what type of thing a map symbol corresponds to.
 Default key is \(oq;\(cq.
@@ -1867,6 +1871,8 @@ option is enabled)
 #enhance
 .lp M-f
 #force
+.lp M-g
+#genocided
 .lp M-i
 #invoke
 .lp M-j