initial creation of a concept of 'active chunks' that are around each

players viewport..obviously they're unique, so it will be refcounted
to handle multiple players
implement operator< for DesiredChunk (which is just a 2d vector basically)

create a map of desired chunks to active chunks, create them if it doesn't
exist each frame (TODO delete them if their refcount is 0, which the refcount
is yet unused).

now onto actually creating the tile physics bodies from within ActiveChunk's
ctor
active chunks are aware of uniqueness now, so they will spawn new ones

from the list of desired chunks for all players, only if they do not exist
already. (temporarily though, it makes about half as many bodies as it should,
for debugging).

it does NOT yet delete bodies/mark chunks as inactive.
fix upper limits on how much can be rendered with the physics renderer
delete gl buffers at dtor (not that we use the dtors during the lifetime

of our game yet)
fix FTBFS from last commit, delete shader in tile renderer at dtor
del tilemap texture at dtor
cleanup tilerenderer unused vars
delete spritesheet textures
handle dtor for gui opengl renderer, destroy buffers
delete fbos and textures in various gl renderers

we don't *yet* destroy the renderers since disconnection isn't implemented,
but when we do, it should be for the most part, leak free. will have to
verify, obviously.
woot, active chunk creation and destruction of tile bodies works beautifully

now i should adjust the tile body amount to properly fill each chunk,
probably adjust chunk size as well, and the size of the virtual viewport.

a huge optimization i think would be instead of using b2Bodys for each
object, use fixtures. requires a good amount of changes though
fix big leak, there's still a minor one here somewhere in the tile

physics loading code but i'm going to try and switch it to fixtures for
other optimization reasons before i hunt that down.
be sure the world dtor deletes a lot more things than it didn't
woot, light at the tunnel, i see fixtures..it's offset and broken though
fix offset
trim active chunk size from 128 to 64

should fix some stuttering for when we create chunks and the fixtures
therein. or perhaps multithread it if it becomes an issue...
reinstate chunk destruction
reinstate contact listener/destruction
shrink chunk considerably