Tutorial: spellcasting

Add some basic spellcasting stuff to the tutorial: read a spellbook,
cast a spell.  If the hero doesn't have enough energy, just adds
a note saying so.

Remove/restore the known spells when entering/leaving the tutorial.

src/decl.c

@@ -372,6 +372,7 @@ static const struct instance_globals_g g_init_g = {
     0L, /* gmst_moves */
     NULL, /* gmst_invent */
     NULL, NULL, NULL, /* gmst_ubak, gmst_disco, gmst_mvitals */
+    { DUMMY }, /* gmst_spl_book */
     /* pline.c */
     UNDEFINED_PTR, /* gamelog */
     /* region.c */

src/nhlua.c

@@ -1695,6 +1695,7 @@ nhl_gamestate(lua_State *L)
         init_uhunger();
         free_tutorial(); /* release gg.gmst_XYZ */
         gg.gmst_stored = FALSE;
+        (void) memcpy(svs.spl_book, gg.gmst_spl_book, sizeof svs.spl_book);
     } else if (!reststate && !gg.gmst_stored) {
         /* store game state */
         gg.gmst_moves = svm.moves;
@@ -1715,6 +1716,8 @@ nhl_gamestate(lua_State *L)
         gg.gmst_mvitals = (genericptr_t) alloc(sizeof svm.mvitals);
         (void) memcpy(gg.gmst_mvitals, (genericptr_t) &svm.mvitals,
                       sizeof svm.mvitals);
+        (void) memcpy(gg.gmst_spl_book, svs.spl_book, sizeof svs.spl_book);
+        (void) memset(svs.spl_book, 0, sizeof(svs.spl_book));
         gg.gmst_stored = TRUE;
     } else {
         impossible("nhl_gamestate: inconsistent state (%s vs %s)",