As discussed with @gabriel-barrett, it definitely no longer makes sense to house the memoset module in coprocessors.

Although memoset::query::Query implements something conceptually like a Coprocessor, it's not identical. We had thought maybe we could still use the Coprocessor mechanism to implement the proving circuits, but that also seems to be a mismatch.

So, to minimize confusion, as we gradually concretize the semantics and lexicon, we decided to re-house memoset entirely. The reason for the new coroutine module is that we think this is the lexical equivalent of coprocessor. It may be that a Coroutine trait emerges, implemented by Query variants. The Coprocessor trait structure won't be directly applicable because of the demands of mutual recursion.

More thought is needed, but the current PR only does the most conservative thing.