+ http: add support for Content-Range and (Byte)-Range headers
+ add RangeDirectives, MultipartByteRanges/Marshallers, multipart-byteranges media-type and UnsatisfiableRange rejection
+ routing: Add ContentRangeSupport to getFromFile()-directive.
= fix code format
= fix HttpHeaderSpecs
= refactoring and cleanup of feature/support-content-range
= renaming AppliedByteRange to AppliedIndexRange and changed index arithmetic to endIndex-exclusive.
= fixes tests FileAndResourceDirectiveSpec with custom RoutingSettings
= simplification of ContentRange invariant requirements
= 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.
Merge pull request #612 from danielwegener/feature/support-content-range

+ Support Range Requests