Extract message interface

Remove pointless aggregate root execute return (might add the event as the return later if there's a good use case).
Tweak planned stream encoder transcoder names
Refactor read stack interfaces and naming

Remove interfaces with a single enumerable property to just use the enumerable interface in it's place.
Start renaming classes to match the sequence validation convention.
TODO: Refactor the sequence validate-able event stream reader implementation to use the idea of stream transcoding like the writer stack.