new 'sortvanquished' option

Allow the preferred sort order for the vanquished monsters list to
be specified in the run-time config file
|OPTIONS=sortvanquished:X
where X is t, d, a, c, n, or z.  It can also be set to 'A' or 'C'
but those aren't documented and aren't offered as choices when
setting the value interactively, which can be done via 'm O' or by
using 'm #vanquished'.

Guidebook.mn has been updated but Guidebook.tex is lagging again.

include/extern.h

@@ -1092,6 +1092,7 @@ extern schar achieve_rank(int);
 extern boolean sokoban_in_play(void);
 extern int do_gamelog(void);
 extern void show_gamelog(int);
+extern int set_vanq_order(void);
 extern int dovanquished(void);
 extern int doborn(void);
 extern void list_vanquished(char, boolean);