anchor.diff:    - document unicode values
     - document how to load theme (with special attention to fonts & images)
     - positional meanings of array items
  +* images
  +  - multiple image width by 0.75 to get point value
  +  - should we use native size of image by default? (after multiplying by 0.75)
  +* implement stem support
  +* rethink how we are handling line heights for fonts, then document carefully
   * dedicated style for top/bottom margin of outline list
   * need dedicated theme styles for paragraph spacings, etc
   * can't put margin top on chapter (chapter_top?)
  
positive.code: 
  * source highlighting (with Pygments) not working inside an admonition block (see chronicles.adoc)
    - *don't need to run source highlighter in dry run*
  * toc
    - make dot leader style separate from title / number
  * running content
  
negative.code: * use padding from theme around block quote content
  * add admonition_label_font_color to theme
  * remove remaining uses of vertical_rhythm and horizontal_rhythm
  * honor safe mode rules
  * allow cover images to be specified by theme as a fallback
  * verify cover image exists; fail gracefully with warning
  * using fallback fonts significantly slows down Prawn because it checks every letter every time (see https://github.com/prawnpdf/prawn/blob/master/lib/prawn/text/formatted/box.rb#L427-L434)
  