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.

Works in principle but awfully slow because of resampling.

not yet tested.

Add export function for OpticNode / Optical.

Not working yet....

Change some function privacy settings.

Fix some doc errors.

Add splitting ratio to Beamsplitter (not used yet).

Add example src-detector.

PaDoublepass example updated accrodingly.

For using reference nodes.

Add port information for NodeDummy & NodeBeamSplitter