This brings nanosvg into the project for SVG loading and rendering.
Unfortunatly we can not at this time use a submodule for this project
until https://github.com/memononen/nanosvg/pull/214 is merged.
This prevents issues like obscure characters getting transformed in symbol
names, resulting in an endless game of whack-a-mole finding symbols that are
replaced, such as 58964ce317.
Instead of duplicating the #defines from the shader into the C code,
this commit adds a custom CMake rule that exports all the #defines
from a shader into a C header.
