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/items/print_item_description.asm

@@ -0,0 +1,31 @@
+PrintItemDescription: ; 0x1c8955
+; Print the description for item [wCurSpecies] at de.
+
+	ld a, [wCurSpecies]
+	cp TM01
+	jr c, .not_a_tm
+
+	ld [wCurItem], a
+	push de
+	farcall GetTMHMItemMove
+	pop hl
+	ld a, [wd265]
+	ld [wCurSpecies], a
+	predef PrintMoveDesc
+	ret
+
+.not_a_tm
+	push de
+	ld hl, ItemDescriptions
+	ld a, [wCurSpecies]
+	dec a
+	ld c, a
+	ld b, 0
+	add hl, bc
+	add hl, bc
+	ld e, [hl]
+	inc hl
+	ld d, [hl]
+	pop hl
+	jp PlaceString
+; 0x1c8987