Remove example trait_test.
Doc fixes.

Separate Dottable trait to additional file.

Various doc work

This simply forwards incoming LightResult.
Rename RefNode::new -> RefNode::from_node to fix clippy warnings.

Function was completely rewritten. Fixed many clippy warnings and
reformatted code.

Add splitting ratio to Beamsplitter (not used yet).

Add example src-detector.

PaDoublepass example updated accrodingly.

For using reference nodes.

Further work on NodeReference (not working yet :-( )