Add connection failure handling to examples

Feature request:

Since htmx heavily relies on client/server interaction, I think that adding an example of how to handle client connection failures would be something that adds value to the project.

It looks like the event that gets emitted for this is: htmx:sendError

Would this be done by listening for this event and then triggering some state in the application like an overlay with a message?

Bonus: Polling the server for connectivity (sending the last failed request) and then removing the connection failure overlay would be useful for a user to know when the app is working again.