Link targets need to be focusable to work with VoiceOver.
Making <main> focusable causes some side-effects, like making the TAB
key go to the beginning of <main> instead of the element after the
currently-clicked region.
Also removes the annoying outline around "main" in some non-mainstream
browsers, without having to add extra CSS.
- Drop copyright symbol: I put it there because certain programs
explicitly look for it, but between rel=license, schema.org microdata,
and creative commons RDFa, I think scrapers should be covered.
- Update the theme-color and friends to work with my site's updated dark
theme.