Better gateway error handling

[kozabrada123]

Currently gateway errors / disconnect aren't handled at all, the gateway just silently disconnects.

Also consider:

Due to Discord's architecture, disconnects are a semi-regular event and should be expected and handled. When your app encounters a disconnect, it will typically be sent a close code which can be used to determine whether you can reconnect and Resume the session, or whether you have to start over and re-Identify.

And we currently have no good way of reconnecting.

Ideally we should have

• an error / disconnect observer
• some sort of auto reconnect maybe (?)