Migration to v0.7

As can be seen there are several rough edges. More boilerplate for simple flows, e.g. the foreach-oncomplete.

The tutorial documentation is not updated yet.
Hmm, what about
~~~scala
val printLines = ForeachSink[String](println)
val materializedFlow =
  FlowFrom(text.split("\\s").toVector)
    .map(_.toUpperCase)
    .withSink(printLines)
    .run()
~~~