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/newlevel.go

@@ -103,7 +103,7 @@ func (g *RogueGame) putThings() {
 			attachObj(&g.Level.Objects, obj)
 			// Put it somewhere
 			obj.Pos, _ = g.findFloor(nil, 0, false)
-			g.Level.SetChar(obj.Pos.Y, obj.Pos.X, obj.Type)
+			g.Level.SetChar(obj.Pos.Y, obj.Pos.X, obj.Kind.Glyph())
 		}
 	}
 	// If he is really deep in the dungeon and he hasn't found the amulet
@@ -114,7 +114,7 @@ func (g *RogueGame) putThings() {
 		obj.Damage = "0x0"
 		obj.HurlDmg = "0x0"
 		obj.Arm = 11
-		obj.Type = Amulet
+		obj.Kind = KindAmulet
 		// Put it somewhere
 		obj.Pos, _ = g.findFloor(nil, 0, false)
 		g.Level.SetChar(obj.Pos.Y, obj.Pos.X, Amulet)
@@ -134,7 +134,7 @@ func (g *RogueGame) treasRoom() {
 		tp := g.newThing()
 		tp.Pos = mp
 		attachObj(&g.Level.Objects, tp)
-		g.Level.SetChar(mp.Y, mp.X, tp.Type)
+		g.Level.SetChar(mp.Y, mp.X, tp.Kind.Glyph())
 	}
 
 	// fill up room with monsters from the next level down