* Move (de)compression helpers to akka-stream #21395
* Move compression and decompression -related classes from
akka-http-experimental to akka-stream
* Add Compression helper object with functions to create
decompressing Flows
* Add a short cookbook entry
* =str move compression impl classes into their own directory (and change visibility)
* =str also expose gzip/deflate compression flows
* Fix formatting of plural ByteStrings in cookbook
* =str #21395 make compressor call Deflater.end in postStop to release resources
Also simplified the creation of the flow given a compressor.
* =str #21395 decompressors call Inflater.end in postStop to release resources
* =str #21395 smallish Scaladoc fixes
* Re enabling Java tests in akka-docs (they were not run before)
* Fixed bug #19764
* #19735 Rewrote every sample using the deprecated PushPullStage and friends
using GraphStage
* Pruned old unused graph images
* Added missing graffle file for new graph images
* 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
