+htp #15920 import DebuggingDirectives from spray
!str switch to a stable `Source.empty` val
=htc small fix and improvements to HttpEntity
!htc #15674 refactor, improve Multipart model
!htp #15674 upgrade to new Multipart model
+str #16093 Add missing runWith variant
Merge pull request #16178 from akka/wip-16093-alternative-runWith-patriknw

+str #16093 Add missing runWith variant
Merge pull request #16183 from spray/wip-15674-mathias

Refactor, improve Multipart model
Merge pull request #16158 from spray/w/15920-DebuggingDirectives

+htp #15920 import DebuggingDirectives from spray
=htp #15920 fix test-case broken because of merge conflict
Merge pull request #16208 from spray/w/15920-DebuggingDirectives

=htp #15920 fix test-case broken because of merge conflict
+str - improves type inference on  by separating the seed from the op (currying)