Fix hovering headings causing page motion

Previously when hovering over headings to expose the permalink and
top-of-page links the height of some headings would change (depending
upon browser) which was visually annoying.

Now a different technique which Shane Baker based on
https://github.com/necolas/normalize.css is used to eliminate the height
issue.

Fixes #289
Add font license summary to LEGAL.rdoc

This makes the full license information in fonts.css more discoverable.

Fixes #290