Hackily copied the moving bbox code into a header.

Also created a wrapper structure which is incredibly
   hacky at the moment but might end up being made
   into a real, sensible wrapper.
Unit-izing Lasercake, commit 1: polygon_collision_detection

polygon_collision_detection.cpp compiles.
The rest of the code doesn't yet.
Merge branch 'master' into unitizing1
comments
re-add tile_size
polygon_collision_detection: fix some temporaries I accidentally left

No behavior change, but it looks reasonable now.
use bounding_box and shape in the global namespace

This might strike the right balance regarding namespace geom.
fix gl_rendering.cpp for units
fix object_and_tile_iteration for units
fix tile_physics.hpp for units
fix main.cpp and main.hpp for units
finish fixing tiles.hpp for units
added new_sunlight_pseudocode.cpp

This won't be a real file; I'm just putting it here
   for posterity / so that I can revision-control it.
more pseudocode; switched to tile-edges-as-shadow-edges

(rather than tile faces or entire tiles
   as shadow edges)
noted some things about the lit_shape structure
Merge branch 'master' into unitizing1

Conflicts:
	data_structures/polygon_collision_detection.cpp
	data_structures/polygon_collision_detection.hpp
fix gl_data_preparation.cpp for units
Merge branch 'master' into unitizing1
refactor world_constants.hpp & add some constants
Merge branch 'master' into unitizing1