anchor.diff:  
   == TODO
   
  +* rename example to basic-example and chronicles to chronicles-example
   * recognize inline image syntax in page_background_image key
   * allow front cover and back cover image to be defined in theme; document in theming-guide
   * keep caption with table (check for sufficient space)
  
positive.code:   - 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
  * add delete_all (or delete_each) method to Array to delete multiple keys
  * 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)
  
negative.code: * honor safe mode rules
  * allow cover images to be specified by theme as a fallback
  * verify cover image exists; fail gracefully with warning
  * stop using fallback fonts in default theme (instead, bundle a fuller font)
    - 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)
  * print scratch.pdf file if verbose / trace mode is on in Asciidoctor
  * introduce setting to indent section content
  * design merge margin logic (like for admonition block)
  