feat: Support non-ID query selector

[shwilliam]

These changes enable support for using <vue-skip-to> to target elements with non-ID selectors. If the to prop passed does not start with a '#', a button will be rendered with a click-handler that will focus the first DOM element that matches the selector.

Before merging, this would need work on:

• [ ] handling compound selectors that start with an ID (eg. '#main.first-paragraph')
• [ ] styling the skip-link button