Consider re-structuring the package

[Andy-Grigg]

Originally raised by @ludovicsteinbach

Some modules have reached unmanageable sizes (queries, _item_results). We could consider splitting them per some logical dimension (IS/RS/Sust or RecordQueries vs BomQueries)

It might be worth having a look at what is part of the public API (by that mean "importable without having to import private modules") and making sure documented classes are part of it