Allow noncontiguous SECTION FRAGMENTs

[Rangi42]

This would address a situation that comes up sometimes in pokered and pokecrystal, where two related chunks of code in a bank have something unrelated in-between them. This has been noted by the in-progress sectionful refactor for pokecrystal.

It would go further toward addressing #244, although this would still apply the same constraints to all FRAGMENTs, which SECTION "Part 2", ROMX, BANK["Part 1"] would presumably not.

[aaaaaa123456789]

At some point this doesn't feel like a fragment. I'd say this would call for a new placement attribute. Perhaps BANK["section"] (instead of a number) to place it in the same bank as some other section?

[Rangi42]

Yes, that's what #244 is requesting. This is different but related. (Consider a function and the data table it uses, separated by some unrelated thing; I'd say those are fragments of the same section.)

[aaaaaa123456789]

The question is, what defines a section, if not contiguity? What you're describing sounds more like a group of sections than like a single section.

[ISSOtm]

I agree that this wouldn't be a fragment anymore, so it would be something else. SECTION FRAGMENT is only intended to allow a given SECTION to span different input files, but that's it, especially given how they're implemented. Since the scope is different, I'd rather have the discussion continue in #244.