Coaleace associations into single arrow

[briggySmalls]

A system, at the zoomed out, top-level view, may have associations between items that represent multiple connections at a low-level view.

For example a user may interact with a hi-fi system in multiple ways: drive volume control, drive input select, receive sound, receive status indicators.

The question is how to represent the implicit relationships. Should the two be connected with a single, no-arrow-headed line? Or two arrows in each direction?

[briggySmalls]

This should be doable, and it should be up to the 'writer' to decide how to represent these relationships.

Mermaid can only do single-headed arrows. PlantUML can do no-headed lines.

But a writer can assess if there are relationships in both directions and choose to represent them accordingly.

Certainly the PlantUML writer should be able to assess if there are associations in both directions between two nodes, and consolodate them into a single no-headed arrow.

Furthermore, in future, where associations are tagged, PlantUML could identify if more than one association connects in a single direction and consolidate into a single, one-directional arrow without a tag

[briggySmalls]

A model now already combine multiple connections with a '...' label (although this is argubly the writer's responsibility).

[briggySmalls]

7f13ad2 moved the '...' logic to the view, where it probably belongs