Add support for anonymous events

[tqwewe]

Adds support for anonymous events, where the handler is inlined in the html.

html! {
    button @click=(|state| state.count += 1) { "Increment" }
}

Upsides:

• Reduces boilerplate for simple events

Downsides:

• Rendered now has a generic
• VSCode intellisense doesn't seem to work in the callbacks
• Cannot manually trigger this event from the server
• Might be harder to debug, since the generated event name is random