Organize the engine/ directory, take 3

Renamed `title` to `movies`.
Moved some functions from `engine/routines/` to their fitting
directories, and cleaned up the base `engine/` directory.
Moved `engine/pokemon/tmhm.asm` back to `engine/items/`.

Made a new subdirectory:
* engine/tilesets: Contains all map-related graphics routines.

engine/events/checksave.asm

@@ -0,0 +1,20 @@
+CheckSave:: ; 4cffe
+	ld a, BANK(sCheckValue1) ; BANK(sCheckValue2)
+	call GetSRAMBank
+	ld a, [sCheckValue1]
+	ld b, a
+	ld a, [sCheckValue2]
+	ld c, a
+	call CloseSRAM
+	ld a, b
+	cp SAVE_CHECK_VALUE_1
+	jr nz, .ok
+	ld a, c
+	cp SAVE_CHECK_VALUE_2
+	jr nz, .ok
+	ld c, $1
+	ret
+
+.ok
+	ld c, $0
+	ret