Replace Reactive Streams to RxJava

[stachu540]

Description

Project Reactor is a way simpler but if this lib wants supporting #19 we need change of Reactive Streams at first and adding #34 support. Probably will after effecting chat and pubsub modules. We won't planning request to supporting WebSocket feature for #19 mentioned on this issue.

Steps to Reproduce

1. Replace Mono responses to Single
2. Replace Flux responses to Flowable
3. Replace FluxProcessor to Observable and using them for processing events
4. Shaping into Android Compatibility #19
5. Prepare to Enhanced Kotlin Support #34

Expected behavior:
All Reactive Streams solutions are be replaced and documented with explanation how it is works.
Actual behavior:
All Reactive Streams are be simplified by Project Reactor
Stacktrace (if applicable):
Reactive Streams prevents to throw exceptions soo with them we can control responses.
Version affected:
0.7.+

Additional Information

Starting March 11 we will abounding Project Reactor and using RxJava 2 with RxAndroid supports. Soo expect this day to test it. 5.0+ is Required!!! because square/okhttp#4481