!par strip down shapeless2 to the bare minimum needed
Merge pull request #15867 from spray/w/strip-down-shapeless

!par strip down shapeless2 to the bare minimum needed
=pro Update the akka version to 2.3.6
=par more shapeless strip-down and comment cleanup

Follow up to #15867.
=str #15852 Port remaining Flow tests to new DSL
Merge pull request #15872 from akka/wip-update-akka-dependencies-to-2.3.6-ban

=pro Update the akka version to 2.3.6
Merge pull request #15837 from drewhk/wip-graph-merge-drewhk

Graph operations merge, broadcast
=str Add some rough overview docs of the new scaladsl package
Merge pull request #15860 from akka/wip-flow-doc-patriknw

=str Add some rough overview docs of the new scaladsl package
=str #15869 Re-enable flow graph checks
Merge pull request #15876 from spray/w/strip-down-shapeless

=par more shapeless strip-down and comment cleanup
Merge pull request #15857 from akka/wip-15852-flow-tests-scaladsl2-ban

=str #15852 Port remaining Flow tests to new DSL
=str make some FlowGraph things akka internal
Merge pull request #15878 from akka/wip-15869-preconditions-patriknw

=str #15869 Re-enable flow graph checks
+str #15764: Add concat and zip combinator