Clojurians Log v2

I've carried out a significant navigation refactor of the https://practical.li/engineering-playbook/, which I think greatly improves the overall structure of the site. The change also moves completely to Zensical, using the new Zensical theme which has a different navigation style. Top level sections are shown as a horizontal navigation bar. There are still many years worth of content from my software engineering career to add. A good structure will help me add more of those experience more effectively. As some pages have moved around, there may be some broken links across the Practicalli websites, which should be resolved in the coming weeks.