PDF slides: optimized layout to avoid clipped text

* Moved the notes to their own right-hand column per suggestion from
  @mef at  https://github.com/hakimel/reveal.js/issues/963#issuecomment-47523839
* Decreased the font sizes a bit so that the slide content would fit
  without clipping.
* Removed the printed HREF from the notes sidebar.
* Made the printed HREF take up its own line so that it's clearer to
  read.