Fix fonts to enable both old-style and lining numerals

CSS is adapted so thet old-style numerals are only used in the
text body, not headings or lists.
Typographical adjustments

- Don't show underline of links by default, but on :hover, :focus
- Add “Syntax” to syntax snippets
- Remove superfluous bullet points from the TOC
- Increase margin-top of h1
Merge pull request #22 from soc/fonts2

Adjustments to typography and design