Anchor bottom-border and :visited state updates

`bottom-border` will now be applied only to anchors inside paragraphs or list items contained within the `.wdn-main` class—effectively, only blocks of text.

Technically, images can still inherit the `bottom-border` if inside a `<p>` or `<li>`, but can be manually removed by applying the `imagelink` class to the `<a>`.

I've also added a darker color (+15%) for `:visited` anchors. (Anchor `:hover` is 10% darker.)