Sanitize data-types for engine end-points and wire descriptions.
Move buffers etc. to Runtime, refactor wire descriptions.
Minor engine reorganization
Switch Interpreter buffers to Values, with appropriate WireDesc.

Values currently have a dummy Read instance, that will need to be
implemented soon.
Move remaining buffer functions into Engine.
First draft of engine refactoring. Both the message loop (processMessage, runMessages, runEngine) and network message processing (runNEndpoint) now live inside the engine. Changes include a MessageProcessor type, a LoopStatus type, and a new Endpoint type. Endpoint notifiers have also been moved, but have yet to be dispatched.
Added dispatching of builtin endpoint notifications.
Merge runtime-refactor work at stable state.