New MPSC Dispatcher especially to address non Unsafe friendly environment.
rename Environment.masterDispatcher : sharedDispatcher
change ringBufferGroup to dispatcherGroup
change default dispatcher to "shared" instead of "ringBuffer" to reflect the fact its the default one and might change type depending on Unsafe avail (Mpsc vs RingBuffer)

 init Stream#cache() to cache a sequence (including complete/error) for new subscribers
Push guaranteed 100% alcohol free. However it might sound a bit scary.
The purpose is to refine packaging for a better visibility amongst new users and avoid conflict with reactor 1.x if present in the classpath (Spring Framework, Spring Integration).