Instead of accessing its reader and writer directly.
TODO: considering add `ReaderWriterCloser` interface and let connection
and stream inherit from it.
- Add `StreamCommunicator` and `RawConnectionCommunicator`, read/write
messages with delim codec, with `IMuxedStream` and `IRawConnection`
respectively.
- Use it in `Multiselect` and `MultiselectClient`.
* ignore kad
* fix swarm, and minor
* fix init and swarm
* ignore pb
* enable mypy
* fix basic host
* fix tcp
* fix mplex
* add typing for pb
* skip format pyi
* [mypy] no need to ignore pb now
* add typing to chat
