Experimental mutation

[Fil Mackay]

I've made an experimental build:

- Implements shared memory, with a shared heap to store member arrays
(strings)
- Uses Reactive Extensions (Rx) - superficial at this stage
- Replace IBatchProducer<T> with System.IObserver<T>, with semantics
of Disruptor adjusted to match
- RingBuffer implements IObservable<T>
- AbstractEvent is back! All event objects inherit from it. This is to
support all the shared memory/heap storage plumbing, as well as the
sequence number. These are pre-filled as before.
- Heap: a light-weight and minimalist heap (stored in shared memory)
to allow strings, and other arrays in event objects.

Still a work-in-progress..

Regards, Fil.