* Very simple implementation, only allows for 1 output socket. As we haven't decided yet whether we keep the XML API, rather not spend more time on this now.
* To use an external osl shader, put the .osl file next to the xml file.
* Parameters: "output" is the output socket name, "output_type" the variable type (float, color and closure color are supported).
Example:
<osl_shader name="tex" src="ramp_closure.osl" output="Phong" output_type="closure color" />
<connect from="tex Phong" to="output surface" />
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