Add an emits option to examples that emit events

[skirtles-code]

Note: There is a CodePen at the bottom of list.md that should be updated to match the code in this PR.

Closes #702.

I have added an emits option to examples that $emit events. This isn't strictly necessary for any of these examples, as they function correctly without it. However, using emits is encouraged elsewhere in the documentation and omitting it can cause problems in situations that are very similar to those in the documentation.

An event listener registered with @ or v-on will be included in the $attrs unless it is listed in the emits. In most cases this does no harm but it does result in a listener being added to the root DOM node of the component. So long as the event name doesn't coincide with a DOM event name this is largely harmless, though wasteful.

Events created by v-model are slightly different. They are not included in the $attrs even if they are omitted from the emits. No listener is added to the DOM node.

However, if a component uses the emits option then it has to list all events, otherwise there'll be a warning logged. So even v-model events will need to be included if a component has any other events. This was why I decided to include emits for all examples, even those using v-model.

A few other notes:

1. Some foo and bar references have been changed.
2. I renamed the event give-advice to advise to dodge the problems around kebab-case vs camelCase (using emits: ['give-advice'] didn't actually work correctly). That's a problem that needs addressing properly and I didn't want to get into it here.
3. I chopped const app = Vue.createApp({}) in a few places where it didn't seem necessary. Note that the other examples on that page weren't using it.
4. I added app.mount('#emit-example-argument') to one example. It was a complete example apart from that one line.

[NataliaTepluhina]

@skirtles-code thank you for these changes! CodePen updated as well 👍🏻