Add and use linmath.h

From https://github.com/datenwolf/linmath.h,
license is "DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE"
Render something at the bottom of a gubbe
Tune the car a bit
Move everything around
Add some help functions for new gl functionality and add glew
as a dependency.
Render the car using a shader.

Nothing fancy for now, and still letting openGL handle
the matrices for us.
Render gubbar using shaders
Render the map using shaders