anchor.diff:  * layout SVG without using keep_together (since we know all the dimensions)
     - fix SVG to a single page (check height + caption height)
   
  +* document that palette-based transparent in PNGs is not supported
  +* document in theming guide what must be done to prepare fonts (old-style 'kern' table, optionally subset) (file issue!)
  +* create document that explains how built-in fonts are generated and what subsets are selected
  +* add broader character range to monospace font so we can drop fallback font by default
  +  - consider having a fallback for prose and fallback for literal
   * file issue for prawn to preserve space (even w/ guards, spaces don't preserve over wrapped lines)
     - if this is fixed, we can remove all the guard indent code
   * file issue for prawn to support spacer fragments with fixed width / height and no text (or text is ignored in calculations)
  
positive.code: 
  * https://code.google.com/p/origami-pdf/[Origami PDF: A PDF inspection library]
  * https://github.com/a1ee9b/PrintPretty[A theme for PDF designed for printing]
  
negative.code: == TODO
  
  * removed scaled width default for image in theme
  * convert "-" in variable name in theme to underscore
  * allow "content" in place of recto_content & verso_content for running header/footer
  * allow dynamic background image with page number in path
  * allow image to span width of page (role=canvas, role=canvas-x or role=canvas-y); if role is canvas or canvas-y, then it does not consume height
  