Tutorial level

Add a tutorial level to teach commands to new players.
Very much a WIP.

Breaks save and bones compat.

include/flag.h

@@ -35,6 +35,7 @@ struct flag {
     boolean goldX;           /* for BUCX filtering, whether gold is X or U */
     boolean help;            /* look in data file for info about stuff */
     boolean tips;            /* show helpful hints? */
+    boolean tutorial;        /* ask if player wants tutorial level? */
     boolean ignintr;         /* ignore interrupts */
     boolean implicit_uncursed; /* maybe omit "uncursed" status in inventory */
     boolean ins_chkpt;       /* checkpoint as appropriate; INSURANCE */