anchor.diff:  * HIGH: put shy marks after dashes to allow wrapping to occur in text justification
   * MEDIUM: auto-space button in btn macro, or add icon & icon placement as attributes on btn macro
   * MEDIUM: move client sniffer JavaScript to file
  +* MEDIUM: use the dfn element for defining a definition of a term (not just term class); see https://developer.mozilla.org/en-US/docs/Web/HTML/Element/dfn
   * QUESTION: add word joiner before inline tags too?
   * packager doesn't resolve include files in subdirectory totally correctly
   * implement checklists
  
positive.code: * recreate ellipses in M+ 1p to be on baseline
  
  .Stylesheet
  * CRITICAL: check style of level 5 and 6 headings (see Groovy docs)
  * CRITICAL: use CSS3 filter scheme that allows admonitions to appear correctly on Google Play Books
    - see if Google Play books supports JavaScript and epubReadingSystem (no, but adds its own class to body)
  
negative.code: * HIGH: add back cover if specified
  * MEDIUM: set modified date explicitly
  * MEDIUM: use function to build and manipulate image paths
  * MEDIUM: issue warning if front-cover-image doesn't match proper syntax
  * support subtitle as separate from main title in package metadata
  * support collection title in package metadata
  
  