Use OPP_ constants separate from trainer constants since
valid opponents can be all Pokemon and trainers

facing directions, npc movement, joypad

rename functions, clean up address/wram comments, other misc
only broken up so that all changes are viewable on github

be on the look out for more static ids in the wild
unused constants are still included because a
script could be written to check whether the player
has picked up an item/fought a legendary etc.