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`.
* Add generic protocol handler
* Add generic protocol handler to stream muxing pipeline
* Modify conn_handler to only deal with connections
* mplex accept stream architecture changes
* Add create generic protocol handler
* Fix minor bugs
* who would win 4 devs or one not
* Debugging
* rearch with handle_incoming infinite loop, seems to work, needs cleanup"
* passing linting, still needs cleanup
* fixing linting again; code still needs cleanup
* fixing tests; code still needs cleanup
* adding test cleanup and task cleanup, removing prints
* linting, and cleanup complete
* storing connections based on peer id
* remove dead code
* remove unnecessary peer_id
