anchor.diff:  
   == TODO
   
  +* add bw / grayscale theme for rouge
   * fix labels in issue tracker to match other projects; in particular, enhancement should be green.
   * setup asciidoctor-mathoid project, then mention it in the STEM support section
   * QUESTION should we show keys with hyphens instead of underscores in theming guide?
  +* add preamble to toc
   
   .1.5.0.alpha.17
  +* don't need to use symbols with alias
  +* document rouge-style in README (already in theming guide, but gets buried)
  +* pass current styles downwards when parsing formatted text (see https://github.com/asciidoctor/asciidoctor-pdf/issues/854)
   * test suite
   * start the README with a proper introduction to Asciidoctor PDF (and not so focused on Prawn)
   * support unnumbered and no-bullet style on ordered list
    ** see https://github.com/asciidoctor/asciidoctor/pull/2286
  -* remove hack to add trailing endline to source for rouge (now fixed in rouge)
  - ** set minimum rouge version
   * implement SVG fit for background image (#765)
   * add helper to expand value into 4 coordinates (top, right, bottom, left)
   
  
positive.code: * should vertical alignment of admonition icon/label should respect padding on content? have it's own padding?
  * allow general settings for admonition icon to be set using admonition_icon key prefix (e.g., admonition_icon_size)
  * allow alignment to be set on discrete heading using role
  * submit pastie theme for Rouge upstream (PR sent, see https://github.com/jneen/rouge/pull/576)
  * SIMPLE: mark required theme keys (assume keys are optional by default)
   ** required keys can never have a null value; most are set by base theme
  * allow font properties to be set for normal paragraph separate from base (need to think about inheritence)
  
negative.code:  ** probably need to introduce a model object to hold the cache
  * line height in TOC is too small if heading only contains monospaced text
  * UPSTREAM: rouge treats a CSS property as a Name::Label instead of a Keyword (see https://github.com/jneen/rouge/issues/665)
  * FIXME: 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)
   ** add broader character range to monospace font so we can drop fallback font by default (#282)
  