Added Parsedown
 - Old parser was not free software. This one now is (MIT license)
 - Also supports GitHub Flavored Markdown https://help.github.com/articles/github-flavored-markdown
 - So now we can add code blocks using the three backticks
Added Prism.js
 - Prism.js is a syntax highlighter
 - Updated colophon to reflect both Prism.js and Parsedown
(m) Re-arrange actions in extlinks plugin