physics seems improved, at least the y value of it is

it's a horrible hack and will need separated out into nice aabb functions
as well as making the entity renderer do that as well, because there's
duplication..and it's very horrible. e.g. i am very inconsistent on
what 'position' refers to. i *think* it's now used as the center in all
scenarios..but i'm not 100% about tiles. i think the x/y index of a tile
indicates the top-left...which makes things sort of odd.
add a bit more buffer b/w sky and ground level. needs less hardcoding

because it's horrible.