Break GLSL shader source out to own files
Initial Stage3D support for GPU-accelerated drawing in Flash

Shaders are converted from GLSL to AGAL with https://github.com/adobe/glsl2agal
and then compiled with the 'AGAL mini assembler', which oddly isn't built in.

Remaining issues:
* scaling is nearest-neighbor
* may show a green line at bottom
* ssllooww on my crappy Atom tablet

Note some fun surprises with Stage3D:
* syntax is slightly different from WebGL just for fun
* textures must be power of 2 sized, so we have to do extra copying
* textures can't be auto-flipped?
* no obvious way to scale up the Stage3D render area from a fixed backing buffer?