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.tex

@@ -1407,6 +1407,11 @@ Default key is `{\tt f}'.
 \item[\tb{\#force}]
 Force a lock. Autocompletes. Default key is `{\tt M-f}'.
 %.lp
+\item[\tb{\#genocided}]
+List any monster types which have been genocided or become extinct.
+Autocompletes.
+Default key is `{\tt M-g}'.
+%.lp
 \item[\tb{\#glance}]
 Show what type of thing a map symbol corresponds to. Default key is `{\tt ;}'.
 %.lp
@@ -2022,6 +2027,9 @@ equivalent is used for another command, so the three key combination
 \item[\tb{M-f}]
 {\tt\#force}
 %.lp
+\item[\tb{M-g}]
+{\tt\#genocided}
+%.lp
 \item[\tb{M-i}]
 {\tt\#invoke}
 %.lp