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/items/updateitemdescription.asm

@@ -0,0 +1,13 @@
+UpdateItemDescription: ; 0x244c3
+	ld a, [wMenuSelection]
+	ld [wCurSpecies], a
+	hlcoord 0, 12
+	ld b, 4
+	ld c, SCREEN_WIDTH - 2
+	call TextBox
+	ld a, [wMenuSelection]
+	cp -1
+	ret z
+	decoord 1, 14
+	farcall PrintItemDescription
+	ret