anchor.diff:  
   * create utility method to get % offset of page as y value (option to constrain to bounds)
   
  +* source highlighting (with Pygments) not working inside an admonition block (see chronicles.adoc)
  +  - don't source highlight in dry run
   * document converter assignment in convert_content_for_block method
   * support transparency for colors
   * support generic color (or value) attribute in formatted text parser instead of specific color systems (rgb, cmyk)
  
positive.code: * introduce setting to indent section content
  * design merge margin logic (like for admonition block)
  * rename default theme to docbook theme, make default the Asciidoctor theme (should we have a base theme?)
  * add callout subs when using CodeRay and when using color themes in Pygments
  * allow relative font size for inline code to be set (perhaps a percentage or em value? there are problems with this in arranger)
  * set defaults in ThemeLoader for required theme settings like prose_margin_top/bottom so we don't need fallbacks in code
  * implement orphan sentences for paragraph
  
negative.code:   - remove unused theme / font files
  * theme keys should be flatted to arbitrary depth
  * enable line above (or below?) title on title page (file issue)
  * text_transform for table foot row
  * file upstream issue for Prawn to warn if it can't resolve a glpyh (or monkeypatch it)
  * make use of shrink_to_fit where appropriate
  