Give item categories and subtypes real types (refactor step 2)

ObjectKind separates what an item is from how it draws: Object.Type
(a byte that doubled as the map character) becomes Kind ObjectKind,
with Glyph() producing the display character and objectKindForGlyph
converting back at the map boundary. KindWand covers the C 'stick'
category. The magic-missile bolt uses KindGold, matching C's literal
o_type='*' trick, with a comment.

PotionKind, ScrollKind, RingKind, WandKind, WeaponKind, ArmorKind and
TrapKind are now iota enums with Stringer (names come from the base
info tables); Object gains typed accessors (obj.RingKind(), ...) and
Launch is typed WeaponKind. beTrapped returns TrapKind. The
getItem/inventory/whatis prompt filters take ObjectKind, with
KindCallable/KindRingOrStick replacing the C CALLABLE/R_OR_S
sentinels; wizard.c's type_name table is subsumed by
ObjectKind.String(). IsRing/IsWearing/initWeapon/doPot signatures are
typed accordingly.

The save format version becomes 5.4.4-go2: the gob field rename would
otherwise silently zero Kind when reading old saves.

No behavior change; full suite green.

game/save_test.go

@@ -83,7 +83,7 @@ func TestSaveRestoreRoundTrip(t *testing.T) {
 		len(h.Player.Pack))
 	found := false
 	for i, o := range h.Player.Pack {
-		t.Logf("  pack[%d]=%p type=%c which=%d", i, o, o.Type, o.Which)
+		t.Logf("  pack[%d]=%p type=%v which=%d", i, o, o.Kind, o.Which)
 		if o == h.Player.CurWeapon {
 			found = true
 		}