Add a basic OSL shader that shows how inputs
and outputs work and do some simple math with
them.
This template is a happy medium between the
templates we already ship, empty_shader is a
little too bare, and the other templates are
a little "too much" and you end up having to
delete a whole bunch of stuff.
a great starting point for some experimentation!
Differential Revision: https://developer.blender.org/D9933
reviewed by: brecht
