* Improve `channel.adoc`: polishing, new channels, java config
* Make `LoadBalancingStrategy` in the `DirectChannel` ctor as
`@Nullable` to reflect the real logic behind
* More Dos and polishing according PR comments
* Mention WebFlux and RSocket endpoints in the `endpoint-summary.adoc`
table
* More reactive streams docs
* `SourcePollingChannelAdapter` polishing
* Wrap multi-value publisher into `Mono.just()` in the `AbstractMessageProducingHandler`
instead of emitting just only a first item for the standard reply
Doc polishing
ad96ca49f1