Started on a new block ID scheme.

-Peter Mawhorter
Switched world.h/c to reference cells instead of blocks, and finished
filling in the beginnings of the block info table. Everything is broken
now.

-Peter Mahworter
Got things to compile after the block/cell split (fixing the segfault
comes next).

-Peter Mawhorter
More debugging. Now it compiles and runs cleanly without any memory
leaks, but everything is just white. Time to actually implement the
dynamic texture atlas functionality.

-Peter Mawhorter
Added a light-yellow shader and got it to compile, load, and run!

-Peter Mawhorter
Things keep working and I'm not sure it's supposed to be this easy. Got
my freetype fonts to render using a relatively simple fragment shader.

-Peter Mawhorter
Got basic "invalid" block textures working.

-Peter Mawhorter