Quasar integration contrib module

This module integrates RxJava with [Quasar](https://github.com/puniverse/quasar) in several ways. It provides:

* A fiber-based scheduler
* A fiber-blocking version of BlockingObservables
* Viewing Quasar channels as Observables and transforming Observables into channels (Quasar channels are a CSP mechanism very similar to channels in the Go programming language).