Update syntax-parse section.

- Fix existing links and add more links.

- Tweak some prose.
Use new Racket 6.0 Scribble CSS as-is.
Regen HTML.

Note: css and js file changes due to using Scribble from Racket 6.0,
which has a new/improved set of CSS styles.
Merge branch 'master' into gh-pages

* master:
  Regen HTML.
  Use new Racket 6.0 Scribble CSS as-is.
  Update syntax-parse section.