Add WebSocket client implementation

[thekid]

Example

use util\cmd\Console;
use websocket\WebSocket;

$remote= $argv[1] ?? 'wss://echo.websocket.events';
Console::writeLine('@@@ Connect ', $remote);
$s= new WebSocket($remote);
$s->connect();

Console::writeLine('<<< ', $s->receive());

$send= $argv[2] ?? 'Test!';
Console::writeLine('>>> ', $send);
$s->send($send);
Console::writeLine('<<< ', $s->receive());

Console::writeLine('>>> Ping');
$s->ping();
Console::writeLine('<<< ', $s->receive());

$s->close();

See https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API

[thekid]

This is a BC break - all Listener implementations with a close() method need to be adapted!

[thekid]

See thekid/crews@3f47d65