Add support for raytracing shader types

[kroppt]

There are more shader types not currently supported:

• ray closest hit shader (.rchit)
• ray any hit shader (.rahit)
• ray miss shader (.rmiss)
• ray generation shader (.rgen)
• ray intersection shader (.rint)

Sascha Willems's Vulkan examples use the listed file extensions for his raytracing shaders. Not sure what else people are currently using.

[svenstaro]

Feel free to add them. :)