The single-request-in-actor-example does not consume the response
in where the status code is not OK. Although this is unlikely
to cause backpressure issues as the response is likely to have
a HttpEntity.Strict entity, the example is confusing as it
does not follow the warning about always consuming the response.
* Sink.seq (Scala DSL) now returns immutable.Seq rather than Seq
* Sink.seq will not silently truncate when incoming elements is > Int.MAX_VALUE
* minor doc fixes
* replacing various grouped(n) / Sink.head with limit(n) / Sink.seq in various tests
* fix inconsistent indentation in RequestParserSpec
