Mpservice

- Removed async streamer.
- Simplified implementation of the `transform` method of streamer.

- Simplify `MPServer.stream`; remove `MPServer.async_stream`; the functionality
of `async_stream` is provided by `stream`.
- Make more utility functions available in `util`.
- Simplify `_async_streamer`.

- `mpservice.http_server` was renamed to `mpservice.http`.
- Initial implementation of socket client/server.

- `mpserver` fine tune, esp about graceful shutdown.
- Use `overrides` to help keep sanity checks on class inheritance.
- Bug fixes in streamer.

- Handle logging in multiprocessing.

- Use 'spawn' method for process creation.
- Refactored and simplified test/build process.
- Removed `mpservice.http_server.run_local_app`.
- Minor bug fixes.