OSL Shaders

My experiments with Open Shading Language shaders, tested in Arnold.

Setup

Your environment should have those variables: (You can set them in houdini.env file)
```
ARNOLD_PLUGIN_PATH = /path/to/this/repo
```

For debugging, add this variable:

OSL_OPTIONS = "range_checking=1,debug_uninit=1,max_warnings_per_thread=100,compile_report=1"