Use OpmResult defined in error module.

Add general OpmResult typedef to error module.

Fix clippy warnings.

Copied from EnergyMeter. Needs modifications yet.

Update docs. Update filter_test example.

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.

not yet tested.

Fix some doc errors.

Add port information for NodeDummy & NodeBeamSplitter