Fix snake_case filenames

Renamed a bunch of files, most of them one-off functions, to better fit
the general snake_case naming scheme. Also renamed some awfully long filenames.

engine/pokemon/level_up_happiness.asm

@@ -0,0 +1,20 @@
+LevelUpHappinessMod: ; 2709e
+	ld a, [wCurPartyMon]
+	ld hl, wPartyMon1CaughtLocation
+	call GetPartyLocation
+	ld a, [hl]
+	and $7f
+	ld d, a
+	ld a, [wMapGroup]
+	ld b, a
+	ld a, [wMapNumber]
+	ld c, a
+	call GetWorldMapLocation
+	cp d
+	ld c, HAPPINESS_GAINLEVEL
+	jr nz, .ok
+	ld c, HAPPINESS_GAINLEVELATHOME
+
+.ok
+	callfar ChangeHappiness
+	ret