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/creature.go

@@ -40,12 +40,12 @@ type Player struct {
 func (c *Creature) On(f CreatureFlags) bool { return c.Flags.Has(f) }
 
 // IsRing is the C ISRING(hand, ring) macro.
-func (p *Player) IsRing(hand, ring int) bool {
-	return p.CurRing[hand] != nil && p.CurRing[hand].Which == ring
+func (p *Player) IsRing(hand int, ring RingKind) bool {
+	return p.CurRing[hand] != nil && p.CurRing[hand].RingKind() == ring
 }
 
 // IsWearing is the C ISWEARING(ring) macro: is the ring on either hand.
-func (p *Player) IsWearing(ring int) bool {
+func (p *Player) IsWearing(ring RingKind) bool {
 	return p.IsRing(Left, ring) || p.IsRing(Right, ring)
 }