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/overworld/load_map_part.asm

@@ -0,0 +1,36 @@
+_LoadMapPart:: ; 4d15b
+	ld hl, wMisc
+	ld a, [wMetatileStandingY]
+	and a
+	jr z, .top_row
+	ld bc, WMISC_WIDTH * 2
+	add hl, bc
+
+.top_row
+	ld a, [wMetatileStandingX]
+	and a
+	jr z, .left_column
+	inc hl
+	inc hl
+
+.left_column
+	decoord 0, 0
+	ld b, SCREEN_HEIGHT
+.loop
+	ld c, SCREEN_WIDTH
+.loop2
+	ld a, [hli]
+	ld [de], a
+	inc de
+	dec c
+	jr nz, .loop2
+	ld a, l
+	add 4
+	ld l, a
+	jr nc, .carry
+	inc h
+
+.carry
+	dec b
+	jr nz, .loop
+	ret