Organize the engine/ directory

This is an informed attempt at reorganizing the engine/ directory by
creating categorized subdirectories, in order to make it easier to
navigate and find things.

The directories created are as follows:
* engine/game: Contains all "minigames", things like the unown puzzle
and slot machine.
* engine/gfx: Contains all handling of graphics. From loading palettes
to playing animations.
* engine/link: Contains all multiplayer functionality.
* engine/menu: Contains all generic/misc. menus and menu code.
Other, more specialized menus are in their own subdirectories (pokedex,
pokegear, party menu, etc).
* engine/overworld: Contains all handling of the overworld. From loading
and connecting maps to wild encounters and the scripting engine.
* engine/pokegear: In the same vein as engine/pokedex, except it could
use some more splitting up.
* engine/pokemon: Contains everything related to manipulating pokemon
data. From the pokemon storage system to evolution and mail.
* engine/printer: Contains everything related to printing things as well
as the printer communication.
* engine/title: Contains intro sequences, title screens and credits.

engine/overworld/tile_events.asm

@@ -0,0 +1,110 @@
+CheckWarpCollision:: ; 1499a
+; Is this tile a warp?
+	ld a, [wPlayerStandingTile]
+	cp COLL_PIT
+	jr z, .warp
+	cp COLL_PIT_68
+	jr z, .warp
+	and $f0
+	cp HI_NYBBLE_WARPS
+	jr z, .warp
+	and a
+	ret
+
+.warp
+	scf
+	ret
+; 149af
+
+CheckDirectionalWarp:: ; 149af
+; If this is a directional warp, clear carry (press the designated button to warp).
+; Else, set carry (immediate warp).
+	ld a, [wPlayerStandingTile]
+	cp COLL_WARP_CARPET_DOWN
+	jr z, .directional
+	cp COLL_WARP_CARPET_LEFT
+	jr z, .directional
+	cp COLL_WARP_CARPET_UP
+	jr z, .directional
+	cp COLL_WARP_CARPET_RIGHT
+	jr z, .directional
+	scf
+	ret
+
+.directional
+	xor a
+	ret
+; 149c6
+
+CheckWarpFacingDown: ; 149c6
+	ld de, 1
+	ld hl, .blocks
+	ld a, [wPlayerStandingTile]
+	call IsInArray
+	ret
+; 149d3
+
+.blocks ; 149d3
+	db COLL_DOOR
+	db COLL_DOOR_79
+	db COLL_STAIRCASE
+	db COLL_STAIRCASE_73
+	db COLL_CAVE
+	db COLL_CAVE_74
+	db COLL_WARP_PANEL
+	db COLL_DOOR_75
+	db COLL_DOOR_7D
+	db -1
+; 149dd
+
+CheckGrassCollision:: ; 149dd
+	ld a, [wPlayerStandingTile]
+	ld hl, .blocks
+	ld de, 1
+	call IsInArray
+	ret
+; 149ea
+
+.blocks ; 149ea
+	db COLL_CUT_08
+	db COLL_TALL_GRASS
+	db COLL_LONG_GRASS
+	db COLL_CUT_28
+	db COLL_WATER
+	db COLL_GRASS_48
+	db COLL_GRASS_49
+	db COLL_GRASS_4A
+	db COLL_GRASS_4B
+	db COLL_GRASS_4C
+	db -1
+; 149f5
+
+CheckCutCollision: ; 149f5
+	ld a, c
+	ld hl, .blocks
+	ld de, 1
+	call IsInArray
+	ret
+; 14a00
+
+.blocks ; 14a00
+	db COLL_CUT_TREE
+	db COLL_CUT_TREE_1A
+	db COLL_TALL_GRASS_10
+	db COLL_TALL_GRASS
+	db COLL_LONG_GRASS
+	db COLL_LONG_GRASS_1C
+	db -1
+; 14a07
+
+GetWarpSFX:: ; 14a07
+	ld a, [wPlayerStandingTile]
+	ld de, SFX_ENTER_DOOR
+	cp COLL_DOOR
+	ret z
+	ld de, SFX_WARP_TO
+	cp COLL_WARP_PANEL
+	ret z
+	ld de, SFX_EXIT_BUILDING
+	ret
+; 14a1a