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/rings.go

@@ -7,12 +7,12 @@ import "fmt"
 // ringOn puts a ring on a hand (rings.c ring_on).
 func (g *RogueGame) ringOn() {
 	p := &g.Player
-	obj := g.getItem("put on", int(Ring))
+	obj := g.getItem("put on", KindRing)
 	// Make certain that it is something that we want to wear
 	if obj == nil {
 		return
 	}
-	if obj.Type != Ring {
+	if obj.Kind != KindRing {
 		if !g.Options.Terse {
 			g.msg("it would be difficult to wrap that around a finger")
 		} else {
@@ -47,7 +47,7 @@ func (g *RogueGame) ringOn() {
 	p.CurRing[ring] = obj
 
 	// Calculate the effect it has on the poor guy.
-	switch obj.Which {
+	switch obj.RingKind() {
 	case RingAddStrength:
 		g.chgStr(obj.Arm)
 	case RingSeeInvisible:
@@ -147,7 +147,7 @@ func (g *RogueGame) ringEat(hand int) int {
 	if ring == nil {
 		return 0
 	}
-	eat := ringUses[ring.Which]
+	eat := ringUses[ring.RingKind()]
 	if eat < 0 {
 		if g.rnd(-eat) == 0 {
 			eat = 1
@@ -155,7 +155,7 @@ func (g *RogueGame) ringEat(hand int) int {
 			eat = 0
 		}
 	}
-	if ring.Which == RingSlowDigestion {
+	if ring.RingKind() == RingSlowDigestion {
 		eat = -eat
 	}
 	return eat
@@ -166,7 +166,7 @@ func ringNum(g *RogueGame, obj *Object) string {
 	if !obj.Flags.Has(Known) {
 		return ""
 	}
-	switch obj.Which {
+	switch obj.RingKind() {
 	case RingProtection, RingAddStrength, RingIncreaseDamage, RingDexterity:
 		return fmt.Sprintf(" [%s]", num(obj.Arm, 0, Ring))
 	}