Small header style correction
Fix the build

* Adds alt attributes to blog images.
* Changes decorative down-arrow image to be specified in css.
* Fix link to mask mag
* Fix hash-link in flock's legal policy
* Switched to using a rake task in order to configure htmlproof to
  accept external links with self-signed certs. (The command line
  htmlproof doesn't expose all available options).
* Configure htmlproof to allow linking to # (the null anchor)