Improve Button Examples

[kaseybon]

The Problem:
Currently the only button example in the pattern library demos an anchor tag. This is fine but doesn't represent the full capabilities of the button component.

The Fix:

1. Update the button component (src/markup/patterns/component/buttons/btn.hbs) to be a button element instead of an anchor tag.
2. Add a new button link component (src/markup/patterns/component/buttons/btn-link.hbs) that uses an anchor tag. This can be a duplicate of the btn.hbs file as we'll need all of the variants that are in the front matter, just be sure to update the name.
3. The following documentation should be added to src/markup/patterns/component/buttons/collection.yaml:

   To ensure keyboard accessibility button and anchor elements should be used when appropriate. If clicking the element will take the user to a different location on the page or to a different page, then use an anchor tag. If clicking the element will trigger a Javascript event, then use a button element.

[vinuch]

id like to take care of this

[kaseybon]

Awesome @vinuch! I've assigned the card to you and I will review your pull request once submitted.

[mahakmakharia]

Should I try my hand at it too?

[kaseybon]

@mahakmakharia I'm sorry for the very late feedback but if you would like to give this a try you are more than welcome to 🙂