Organize the engine/ directory, take 2

Renamed `game` to `games` and `menu` to `menus`.
Moved some functions from `engine/routines/` to their fitting subdirectories.

Made two new subdirectories:
* engine/rtc: Contains all RTC-related things. Menus, hardware, misc
functions.
* engine/items: Contains all item-related things. Pack, item effects,
other item handlers.

engine/overworld/loadmappart.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