Support ping/pong control frames

[bradleyayers]

I've written a server that sends pings messages to clients, in order to detect broken connections, and I'd like to use wsta to interact with it. However it seems that wsta does not send pong messages in response to pings.

In my opinion wsta should (by default) reply to ping messages with pong, by just replying with the ping payload.

The current options for "ping" (e.g. -p) are a little confusing, since they're really just sending plain messages as opposed to ping frames.

[eliihen]

Hi,

Yes, I've wanted to implement this before, but not had the time. rust-websocket supports this, so it is possible to do without much effort.

We probably should bring the project up to date with its dependencies first, though, which is a fair bit of work in itself.