add a couple testing worlds
OpenGL: refactor: use the expected matrices.
Use glm OpenGL math library; use it to stop using GLU.

GLU is not part of OpenGL ES implementations;
glm offers the GLSL mathematics functions;
glm will probably be useful in other ways in the
graphics code too.
refactor GL data passing around
add bundled GLM option, and properly CMakeLists.txt it
Implement view frustum culling of tiles.

This speeds up `spiky` by a factor of 3 for me.