Use cases of `multi-residue` `_ihm_model_representation_details.model_granularity`

[aozalevsky]

I couldn't find examples of multi-residue granularity. It seems that in all relevant entries (like NPC), it was replaced with by-feature. I think documentation regarding the selection of by-residue, multi-residue, and by-feature need some clarification of the intended use. Also by-residue states:

coordinates represent the alpha carbon position of a residue

Which seems unnecessary protein-specific.