Q #1: Should this be in uasyncio package at all? Upstream doesn't have
this. Pro: will be easier for people do discover (see e.g.
#148)

Q #2: This provides implements 2 ways to create a WS connections:

1. using start_ws_server(); 2) using wrapping existing StreamReader
   and StreamWriter. History: initial prototype of course used 2). But
   the idea was "it should be like the official start_server()!!1". But
   then I though how to integrate it e.g. with Picoweb, and became clear
   that 2) is the most flixble way. So, 1) is intended to be removed.

Q #3: Uses native websocket module for read path, but has own
write path due to micropython/micropython#3396

Q #4: Requires #227
due to micropython/micropython#3394 .