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/engine_flags.asm

@@ -0,0 +1,86 @@
+EngineFlagAction:: ; 80430
+; Do action b on engine flag de
+;
+;   b = 0: reset flag
+;     = 1: set flag
+;     > 1: check flag, result in c
+;
+; Setting/resetting does not return a result.
+
+
+; 16-bit flag ids are considered invalid, but it's nice
+; to know that the infrastructure is there.
+
+	ld a, d
+	cp 0
+	jr z, .ceiling
+	jr c, .read ; cp 0 can't set carry!
+	jr .invalid
+
+; There are only $a2 engine flags, so
+; anything beyond that is invalid too.
+
+.ceiling
+	ld a, e
+	cp NUM_ENGINE_FLAGS
+	jr c, .read
+
+; Invalid flags are treated as flag 00.
+
+.invalid
+	xor a
+	ld e, a
+	ld d, a
+
+; Get this flag's location.
+
+.read
+	ld hl, EngineFlags
+; location
+	add hl, de
+	add hl, de
+; bit
+	add hl, de
+
+; location
+	ld e, [hl]
+	inc hl
+	ld d, [hl]
+	inc hl
+; bit
+	ld c, [hl]
+
+; What are we doing with this flag?
+
+	ld a, b
+	cp 1
+	jr c, .reset ; b = 0
+	jr z, .set   ; b = 1
+
+; Return the given flag in c.
+.check
+	ld a, [de]
+	and c
+	ld c, a
+	ret
+
+; Set the given flag.
+.set
+	ld a, [de]
+	or c
+	ld [de], a
+	ret
+
+; Reset the given flag.
+.reset
+	ld a, c
+	cpl ; AND all bits except the one in question
+	ld c, a
+	ld a, [de]
+	and c
+	ld [de], a
+	ret
+; 80462
+
+
+INCLUDE "data/engine_flags.asm"