Copied from EnergyMeter. Needs modifications yet.

Update docs. Update filter_test example.

Update documentation.

Tiny doc fixes.

Add serde_yaml crate and add Serialize to spectrum.

Doc work.
Remove no unsed function in Light.

Make some functions private.

If a port mapping was defined and group noed connected afterwards,
port maps might become invalid.

Check now if input / output nodes are half-connected.
Add unit tests accordingly.

To be used for improved port mapping.

Not yet tested at all.

Various doc work

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

The node RealLens is missing in the repo..

Remove some debug meassages. Improve spectrum plot, code cleanups.