anchor.diff:  * make alternating page title position optional (via theme?)
   * BUG: page numbers are off in Clojure Cookbook
   * image in header / banner (need to implement a masthead)
  -* do CMYK values work for colors?
  +* do CMYK values work for colors? no, but we should support an array value
   * fix passthrough placeholders that get caught up in syntax highlighting (see https://github.com/asciidoctor/asciidoctor/blob/master/test/blocks_test.rb#L2258-L2277)
  +* we could eliminate some of the tags we're currently matching in the formatted text parser (e.g., link)
  +* add Preamble to TOC
  +* NOTE prawn-svg supports loading from a URI
   
   * enable pagenums attribute by default (may require changes to how we handle attributes)
   * start page numbering on first page if no title page
  
positive.code: * list bullet in ordered list needs to grow with length of number
  * document how the treetop parser is rebuilt
  * rewrite optimize-pdf using rghost
  * 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)
  * enable fallback font (Golo guide has problem with License block)
  
negative.code: * reorg Prawn extensions (see prawn-table for example)
  * rename "theme" to "style"?
  * restrict custom theme path to jail (or load from load_path)
  * implement convert_toc
  * can get orphan conum if starts on last line of page (fixed already?)
  * only create title page if doctype=book
  