anchor.diff:  * create proper default (Asciidoctor) theme
   * list bullet in ordered list needs to grow with length of number
   * document how the treetop parser is rebuilt
  -* rewrite optimize-pdf using rghost
  -  - add Optimizer class; wire to cli
   * 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)
   * padding top and bottom on content affects height_of calculations (need to review)
  
positive.code: * separate theme control for listing vs literal block (and maybe source too)
  * allow title page image "bottom" to be set instead of "top" (mutually exclusive)
  
  * pass macro doesn't work in source block when macro subs and highlighting are both enabled
  * bind image_registry between scratch and main document so we don't process the same image more than once
    - need to do some testing
  
negative.code: 
  * uncompress PNG files
  * avoid the fallback font if possible (use full fonts in your theme)
  * font families used in SVGs must match keys in the font catalog
  
  == Open Questions
  
  