anchor.diff:  * refactor as Prawn view to avoid method name conflicts (also see https://github.com/prawnpdf/prawn/issues/802)
   * make CodeRay theme colors configurable (in theme?)
   * create proper default (Asciidoctor) theme
  -* list bullet in ordered list needs to grow with length of number
   * document how the treetop parser is rebuilt
   * use ImageMagick to uncompress PNG images before reading them (could also just document this)
   * rework font so we can set actual height, calculate x_height internally (use 1em for spacings)
  
positive.code: * support !include in theme file (file issue)
  * margin per heading level (see https://github.com/asciidoctor/asciidoctor-pdf/issues/176)
  * add cover page example to chronicles so people see how to use it
  * images
    - multiple image width by 0.75 to get point value (including in running header and footer)
    - should we use native size of image by default? (after multiplying by 0.75)
  * don't orphan a single line of paragraph (send it with a buddy line)
  * implement stem support
  * fail gracefully if theme file cannot be found
  * dedicated style for top/bottom margin of outline list
    - allow margin top and bottom to be set for lists (applies to outer-most list)
    - allow spacing between nested lists levels be configured in theme
  
negative.code: 
  == TODO
  
  * convert image width to points for images on title page and in running header and footer; add support for pdfwidth
  * upgrade Treetop
  * rename example to basic-example and chronicles to chronicles-example
  * recognize inline image syntax in page_background_image key
  