Add @vue-slot and @vue-event annotation to document slots and emitted events

[pbastowski]

Update: I see that I should probably have added this to #102.

This is a proposal to extend jsdoc-vuejs with two new annotations:

@vue-slot
@vue-event

I need to document slots and events that are offered by my components. jsdoc does not have a suitable annotation for slots. There is the @emits annotation, but it does not work well for events, as it does not have a way to document the event's parameters (that I know of).

Both slots (scoped) and events (params) have an ability to pass parameters. It would be great if we had a @vue-slot and @vue-event annotation, which would allow us to follow it with @param annotations. @params would then describe the slots and events for us. The result would be a table for slots and a separate table for events.

For example

/**
 * The s-popup component displays a popup window with your text and an optional title.
 * 
 * @vue-slot activator Clicking this content will display the popup
 * @param {object} item This is purely fictional, just to demonstrate how the @param would be used
 *
 * @vue-slot [title] An optional popup title
 * @vue-slot default The content to be displayed
 *
 * @vue-event close
 * @param {string} result The button that the user clicked (OK or Cancel)
 * 

Is this feasible?

[pbastowski]

Closing in favor of #102