Scaled up all of the entities (effectively reducing cell size). Cells
are now roughly 1/3 of a meter on a side.

-Peter Mawhorter
Got the unit tests working again and messed with the branches generator
to make it work much better (also added some parameters).

-Peter Mawhorter
Implemented basic block geometry functionality, which involved
parameterizing the face-pushing functions in display.c. Also implemented
a logarithmic depth buffer to get rid of z-fighting issues, which allows
me to put grass from above a dirt block onto the face of the dirt block
with only very minor visual artifacts (dirt-colored seams). Grass and
grass roots are now working once more.

-Peter Mawhorter
Added a Bezier curve representation; worked towards plant generation
starting with simple Minecraft-like leaves (still some ways to go).

-Peter Mawhorter
Some more (partial) work on plant texture generation.

-Peter Mawhorter