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/select_menu.asm

@@ -0,0 +1,191 @@
+SelectMenu:: ; 13327
+
+	call CheckRegisteredItem
+	jr c, .NotRegistered
+	jp UseRegisteredItem
+
+.NotRegistered:
+	call OpenText
+	ld b, BANK(ItemMayBeRegisteredText)
+	ld hl, ItemMayBeRegisteredText
+	call MapTextbox
+	call WaitButton
+	jp CloseText
+; 13340
+
+
+ItemMayBeRegisteredText: ; 13340
+	text_jump UnknownText_0x1c1cf3
+	db "@"
+; 13345
+
+
+CheckRegisteredItem: ; 13345
+
+	ld a, [wWhichRegisteredItem]
+	and a
+	jr z, .NoRegisteredItem
+	and REGISTERED_POCKET
+	rlca
+	rlca
+	ld hl, .Pockets
+	rst JumpTable
+	ret
+
+.Pockets:
+; entries correspond to *_POCKET constants
+	dw .CheckItem
+	dw .CheckBall
+	dw .CheckKeyItem
+	dw .CheckTMHM
+
+.CheckItem:
+	ld hl, wNumItems
+	call .CheckRegisteredNo
+	jr c, .NoRegisteredItem
+	inc hl
+	ld e, a
+	ld d, 0
+	add hl, de
+	add hl, de
+	call .IsSameItem
+	jr c, .NoRegisteredItem
+	and a
+	ret
+
+.CheckKeyItem:
+	ld a, [wRegisteredItem]
+	ld hl, wKeyItems
+	ld de, 1
+	call IsInArray
+	jr nc, .NoRegisteredItem
+	ld a, [wRegisteredItem]
+	ld [wCurItem], a
+	and a
+	ret
+
+.CheckBall:
+	ld hl, wNumBalls
+	call .CheckRegisteredNo
+	jr nc, .NoRegisteredItem
+	inc hl
+	ld e, a
+	ld d, 0
+	add hl, de
+	add hl, de
+	call .IsSameItem
+	jr c, .NoRegisteredItem
+	ret
+
+.CheckTMHM:
+	jr .NoRegisteredItem
+
+.NoRegisteredItem:
+	xor a
+	ld [wWhichRegisteredItem], a
+	ld [wRegisteredItem], a
+	scf
+	ret
+; 133a6
+
+
+.CheckRegisteredNo: ; 133a6
+	ld a, [wWhichRegisteredItem]
+	and REGISTERED_NUMBER
+	dec a
+	cp [hl]
+	jr nc, .NotEnoughItems
+	ld [wCurItemQuantity], a
+	and a
+	ret
+
+.NotEnoughItems:
+	scf
+	ret
+; 133b6
+
+
+.IsSameItem: ; 133b6
+	ld a, [wRegisteredItem]
+	cp [hl]
+	jr nz, .NotSameItem
+	ld [wCurItem], a
+	and a
+	ret
+
+.NotSameItem:
+	scf
+	ret
+; 133c3
+
+
+UseRegisteredItem: ; 133c3
+
+	farcall CheckItemMenu
+	ld a, [wItemAttributeParamBuffer]
+	ld hl, .SwitchTo
+	rst JumpTable
+	ret
+
+.SwitchTo:
+; entries correspond to ITEMMENU_* constants
+	dw .CantUse
+	dw .NoFunction
+	dw .NoFunction
+	dw .NoFunction
+	dw .Current
+	dw .Party
+	dw .Overworld
+; 133df
+
+.NoFunction: ; 133df
+	call OpenText
+	call CantUseItem
+	call CloseText
+	and a
+	ret
+; 133ea
+
+.Current: ; 133ea
+	call OpenText
+	call DoItemEffect
+	call CloseText
+	and a
+	ret
+; 133f5
+
+.Party: ; 133f5
+	call RefreshScreen
+	call FadeToMenu
+	call DoItemEffect
+	call CloseSubmenu
+	call CloseText
+	and a
+	ret
+; 13406
+
+.Overworld: ; 13406
+	call RefreshScreen
+	ld a, 1
+	ld [wUsingItemWithSelect], a
+	call DoItemEffect
+	xor a
+	ld [wUsingItemWithSelect], a
+	ld a, [wItemEffectSucceeded]
+	cp 1
+	jr nz, ._cantuse
+	scf
+	ld a, HMENURETURN_SCRIPT
+	ld [hMenuReturn], a
+	ret
+; 13422
+
+.CantUse: ; 13422
+	call RefreshScreen
+
+._cantuse
+	call CantUseItem
+	call CloseText
+	and a
+	ret
+; 1342d