Updated the Lommel-Seeliger / Oren-Nayar branch with all the latest 
v3.8.0-alpha features, and released it under a new designation:

https://github.com/POV-Ray/povray/releases/tag/v3.8.0-x.10021928


The `v3.8.0-x.NUMBER` designation is not intended to specifically denote 
this pair of features, but rather a particular collection of additional 
features quite likely to undergo further compatibility-breaking changes 
before integration into the official development branch, but at the same 
time highly unlikely to be ditched again. Lommel-Seeliger and Oren-Nayar 
just happen to be the first such features to be in this branch.


For example, with the Oren-Nayar diffuse model I am not sure yet whether 
the parameter should specify the /standard deviation/ (sigma) or the 
/variance/ (sigma squared) of the microfacets orientation. A comparison 
with the parameterization used by other renderers (Blender maybe?) could 
be of use there.

Also, the interaction between both new models and the `fresnel` feature 
may still be subject to change; the current behaviour is simply emergent 
from the simplest implementation, and may not be the most useful.

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