Changed rules:
* 1.9 Always onSubscribe prior to any other signals
* 1.9 NullPointerException if subscriber is null
* 3.17 Long overflow, effectively unbounded instead of onError
Fixed some more things:
* fixed some FIXME
* Long drop and take
* memory leaks in tck tests, use BeforeClass to create ActorSystem
use AfterClass to shutdown ActorSystem
* more tck tests
* don't emit OnComplete when substream is cancelled
* work around for memory leak in PrefixAndTail
* add supervion for stages and built in ops run by interpreter
* add supervision for mapAsync and mapAsyncUnordered
* add supervision to groupBy and splitWhen
* reference doc for scala and java
* replace all existing Transformer with Stage (PushPullStage)
* use Flow[ByteString, ByteString] as encoder/decoder transformer in http
* use the IteratorInterpreter for strict if possible
* emit then become
* emit then finish
* termination emits
* FlowTransformerSpec
* rework types to work with Java API
* rename and move things
* add scaladoc
- Switches from using size-of-1/2 Vectors to using Lists
- Fixes an issue where processorForNode wouldn't use the dispatcher form the settings
- Adds a dedicated Collect fusion op
- Adds various simplifications to ActorBasedFlowMaterializer
- Adds FIXMEs where appropriate
- Switches `grouped` to use a VectorBuilder
- Adds support for `scan`
- ActorBasedFlowMaterializer now uses Iterator instead of head+tail decomp on Seqs
- Identity and Completed Transformers are now cached
- Adds dedicated AstNodes for all combinators
- Adds a hook-in point for fusion in `ActorBasedFlowMaterializer`
- Adds support for `Operate` an AstNode with a function that create a fusing.Op
- Adds experimental and slow optimizer as a PoC
- Adds verification that Ast.Fused does not exist in optimizer input
