Fixed my various math bugs.

  - Pandoc was being run twice on the posts—both before and after making the snapshot
  - fixed system to only ever run Pandoc *after* the snapshot
  - wrote new teaserField that works on the item rather than a snapshot
Continued working on my Tree Edit Distance article.

  - added the dynamic programming version of the algorithm
  - wrote a version converting the lists to arrays for faster lookup
  - added an aside about using lists as loops