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.

# Conflicts:
#	constants/map_constants.asm
#	constants/wram_constants.asm
#	data/radio/oaks_pkmn_talk_routes.asm
#	data/radio/pnp_hidden_places.asm
#	engine/battle/core.asm
#	engine/breeding.asm
#	engine/phone/phone_scripts.asm
#	engine/radio.asm
#	maps/BattleTower1F.asm
#	maps/OlivineLighthouse2F.asm
#	maps/OlivineLighthouse6F.asm
#	maps/PokemonFanClub.asm
#	maps/RadioTower1F.asm
#	maps/RadioTower2F.asm
#	maps/Route30BerryHouse.asm
#	maps/Route34IlexForestGate.asm
#	maps/Route36NationalParkGate.asm
#	maps/RuinsOfAlphKabutoChamber.asm
#	maps/RuinsOfAlphResearchCenter.asm
#	maps/VermilionPort.asm
#	maps/VictoryRoad.asm

Since we're aiming for consistency across the codebase, I believe it
includes a uniform way to refer to the creatures this game consists of
in the labels of the code.
The only exceptions to this rule are labels referring to things named
through the use of the <PK><MN> or <PKMN> characters, in which case PKMN
is used.

Most of this was already consistent enough™, I just picked the
convention with the most occurences and fixed the outliers.

# Conflicts:
#	audio/engine.asm
#	constants/gfx_constants.asm
#	constants/map_data_constants.asm
#	constants/pokemon_data_constants.asm
#	constants/sprite_constants.asm
#	constants/wram_constants.asm
#	data/maps/data.asm
#	engine/battle/ai/scoring.asm
#	engine/battle/core.asm
#	engine/battle/effect_commands.asm
#	engine/battle/misc.asm
#	engine/battle_anims/getpokeballwobble.asm
#	engine/breeding.asm
#	engine/buy_sell_toss.asm
#	engine/decorations.asm
#	engine/events/battle_tower/battle_tower.asm
#	engine/events/battle_tower/rules.asm
#	engine/events/buena.asm
#	engine/events/bug_contest/contest_2.asm
#	engine/events/daycare.asm
#	engine/events/dratini.asm
#	engine/events/halloffame.asm
#	engine/events/happiness_egg.asm
#	engine/events/kurt.asm
#	engine/events/lucky_number.asm
#	engine/events/magnet_train.asm
#	engine/events/overworld.asm
#	engine/events/pokerus/pokerus.asm
#	engine/events/print_unown.asm
#	engine/events/print_unown_2.asm
#	engine/events/unown_walls.asm
#	engine/item_effects.asm
#	engine/link.asm
#	engine/mon_menu.asm
#	engine/player_object.asm
#	engine/routines/playslowcry.asm
#	engine/scripting.asm
#	engine/search.asm
#	engine/search2.asm
#	engine/specials.asm
#	engine/start_menu.asm
#	engine/timeset.asm
#	home/battle_vars.asm
#	home/map.asm
#	maps/GoldenrodUndergroundSwitchRoomEntrances.asm
#	maps/IlexForest.asm
#	maps/KrissHouse2F.asm
#	maps/Route39Barn.asm
#	mobile/mobile_12_2.asm
#	mobile/mobile_40.asm
#	mobile/mobile_5f.asm
#	wram.asm

# Conflicts:
#	data/player_names.asm
#	engine/battle/menu.asm
#	engine/billspc.asm
#	engine/billspctop.asm
#	engine/buy_sell_toss.asm
#	engine/decorations.asm
#	engine/delete_save_change_clock.asm
#	engine/events/buena.asm
#	engine/events/elevator.asm
#	engine/events/kurt.asm
#	engine/events/mom.asm
#	engine/events/move_tutor.asm
#	engine/events/pokecenter_pc.asm
#	engine/events/pokepic.asm
#	engine/events/std_scripts.asm
#	engine/events/unown_walls.asm
#	engine/init_gender.asm
#	engine/intro_menu.asm
#	engine/mail.asm
#	engine/main_menu.asm
#	engine/mart.asm
#	engine/menu_2.asm
#	engine/mon_menu.asm
#	engine/pack.asm
#	engine/slot_machine.asm
#	engine/start_menu.asm
#	home/menu.asm
#	maps/CeladonDeptStore6F.asm
#	maps/CeladonGameCornerPrizeRoom.asm
#	maps/DragonShrine.asm
#	maps/EarlsPokemonAcademy.asm
#	maps/GoldenrodCity.asm
#	maps/GoldenrodDeptStore6F.asm
#	maps/GoldenrodGameCorner.asm
#	maps/GoldenrodPokeComCenter2FMobile.asm
#	mobile/mobile_12.asm
#	mobile/mobile_12_2.asm
#	mobile/mobile_22.asm
#	mobile/mobile_22_2.asm
#	mobile/mobile_40.asm
#	mobile/mobile_45.asm
#	mobile/mobile_45_sprite_engine.asm
#	mobile/mobile_46.asm
#	mobile/mobile_5c.asm
#	mobile/mobile_5f.asm
#	mobile/mobile_menu.asm

# Conflicts:
#	data/items/descriptions.asm
#	data/sprite_anims/framesets.asm
#	engine/crystal_colors.asm
#	engine/events/kurt.asm
#	engine/events/special.asm
#	engine/events/std_scripts.asm
#	engine/events_3.asm
#	engine/item_effects.asm
#	engine/namingscreen.asm
#	engine/scripting.asm
#	engine/stats_screen.asm
#	engine/trade_animation.asm
#	home/audio.asm
#	main.asm
#	maps/BattleTower1F.asm
#	maps/BattleTowerBattleRoom.asm
#	maps/BurnedTowerB1F.asm
#	maps/ElmsLab.asm
#	maps/GoldenrodDeptStore5F.asm
#	maps/GoldenrodUnderground.asm
#	maps/HallOfFame.asm
#	maps/MahoganyTown.asm
#	maps/ManiasHouse.asm
#	maps/MobileBattleRoom.asm
#	maps/MobileTradeRoomMobile.asm
#	maps/RadioTower2F.asm
#	maps/Route35NationalParkGate.asm
#	maps/Route36NationalParkGate.asm
#	maps/Route39Farmhouse.asm
#	tilesets/palette_maps.asm

Added a bunch of constants for the bitflags of each kind of menu. Some
are slightly vague or too long, but I'm not sure how to else name them.