Update ws example

[mattlink]

Adds another endpoint to examples/basic_ws.py which illustrates how to read data from the websocket.

It is not clear from the existing example (or docs, currently) that you can specify a data argument to the handler function to effectively get the contents of ws.receive(). There are other hidden arguments which seem to correspond to these annotations

[jph00]

Thanks - this is a good idea. I guess it also probably needs something on the page demonstrating its use?

[jph00]

@mattlink just bumping this...