Added shortcode for links to page anchors.

- The shortcode "anchor-link" takes an anchor name and creates a link to the
  current page (using its permalink) at that anchor (for example, given
  "anchor1", it might produce "http://www.example.com#anchor1"). This may be
  used to create anchor links which will work properly when clicked from a
  summary by loading the full article and starting the page scroll at that
  anchor.