Add the ablity to restart broken connection.

[smimram]

With the webcam example (#25), liquidsoap's harbor sometimes stops with

2022/08/25 11:07:54 [input.harbor_0:2] Feeding stopped: Ffmpeg_decoder.End_of_file.

and in the browser's console we get

The connection to ws://localhost:8000/mount was interrupted while the page was loading.

Webcast.js should provide a simple way to catch websocket's errors and initiate a new connection.

[toots]

The underlying websocket should be present on the webcast's instance:

webcast.socket.on("error", ...);
webcast.socket.on("close", ...);

Is that enough for you?

[smimram]

The thing is that most of the connection stuff is performed by the constructor, which makes it uneasy to reconnect. Let me propose something to you...

[smimram]

Actually the main problem is that we cannot catch error performed when constructor's code is executed. I propose #27 to solve this.