ShaderFX next steps

[tebjan]

since the proof of concept is now working, we can think of next steps:

• [ ] control flow regions see vvvv/VL.StandardLibs#613
• [ ] shader source class from string to avoid implementing all nodes for all types as individual shader files
• [x] make a shader node factory from xenkos hlsl definitions now: vvvv/VL.StandardLibs#194