= can: refactor range support model in preparation for coming akka-http migration

All seemingly breaking changes that this commit introduces only affect recently added structures and are therefore neutral with respect to the last release.
= httpx: DRY up (un)marshallers for `multipart/byteranges`

All seemingly breaking changes that this commit introduces only affect recently added structures and are therefore neutral with respect to the last release.
= routing: upgrade to latest spray-http refactoring, tweak and add a few more tests

All seemingly breaking changes that this commit introduces only affect recently added structures and are therefore neutral with respect to the last release.