Mpservice

- Make `StopRequested` inherit from `BaseException` instead of `Exception`.
- Finetune printout of exception info in process and threads.

- Removed module `mpservice.rate_limiter` (moved to package `cloudly`).
- Bug fix regarding `mpservice.mpserver.Worker.preprocess`--now Exception objects are not sent to `preprocess`.

- `mpservice.streamer.Parmapper` gets new parameter `preprocessor`, which is passed on to `fifo_stream`.
- `ProcessRunner` and `ProcessRunee` are moved from `mpservice.streamer` into `mpservice.multiprocessing.runner`.
- `RateLimiter` and `AsyncRateLimiter` are moved from `mpservice.streamer` into `mpservice.rate_limiter`.

- Classes `Tailor` and `AsyncTailor` were renamed to `Tailer` and `AsyncTailer`.
- `mpservice.streamer.{fifo_stream, async_fifo_stream}` get new parameter `preprocessor`.
- `mpservice.mpserver.{Server, AsyncServer}.stream` parameter `preprocess` was renamed to `preprocessor`,
and they are now simply passed on to `fifo_stream` or `async_fifo_stream`.
- New class `mpservice.streamer.AsyncRateLimiter`.

- New class `mpservice.streamer.RateLimiter`.

- Further separate "async_streamer" from "streamer" because I doubt "async_streamer" has a strong use case.
- Update documentation for "streamer".
- Requires Python 3.10.