Parses the render options that would be used to
follow the given link, but does not render.
Example
Given a link with some [up-...] attributes:
<a href="/foo" up-target=".content" up-layer="new">...</a>
We can parse the link's render options like this:
let link = document.querySelector('a[href="/foo"]')
let options = up.link.followOptions(link)
// => { url: '/foo', method: 'GET', target: '.content', layer: 'new', ... }
