anchor.diff:  = WORKLOG
   
   * use Groovy language specification as case study to find corner cases
  +  - perhaps progit2 as well; others?
   
   == TODO
   
  -* utility method to get % offset of page as y value (option to constrain to bounds)
  -* prevent title-logo-image from spilling to next page
  -* make revision info delimiter configurable in theme
  -* implement per-document title page background image (final fix for #134)
  +* create utility method to get % offset of page as y value (option to constrain to bounds)
   
  -* allow theme_font to set line_height (honor this setting from document)
  +* **allow theme_font to set line_height** (honor this setting from document)
     - theme setting for code line height (currently using base_line_height)
  +* implement convert_inline_indexterm (as noop; just to silence the warning)
  +* use docdate attribute to set modification date on document (file issue)
  +* more theme control over toc (font size, style, color per level)
  +* prevent title-logo-image from spilling to next page (same with title content)
  +* support font family and style for heading level
   * remove .to_s calls on color values now that theme normalizes them (perhaps should be a post-load theme procedure)
  +  - do CMYK values work for colors? no, but we should support an array value
   * split prawn_ext/extensions.rb into individual modules and include them
  -* code cleanups (constants and such)
  +* code cleanups (regexps to constants, nil? checks and such)
  +  - extract regex in ThemeLoader into constant
   * theme keys should be flatted to arbitrary depth
   * enable line above (or below?) title on title page (file issue)
   * quote all color values in reference themes
  -* extract regex in ThemeLoader into constant
   * allow pdf-page-layout (portrait || landscape) to be set in document
   * attribute or role to control table shading (all, even, odd) (or call it striped like bootstrap?)
   * make conum glyphs configurable in theme (use reference table to resolve)
  
positive.code: * document how the treetop parser is rebuilt
  * rewrite optimize-pdf using rghost
    - add Optimizer class; wire to cli
  * 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: * add admonition_label_font_color to theme
  * remove remaining uses of vertical_rhythm and horizontal_rhythm
  * implement subtitle on title page
  * allow cover images to be specified by theme as a fallback
  * verify cover image exists; fail gracefully with warning
  * print scratch.pdf file if verbose / trace mode is on in Asciidoctor
  * introduce setting to indent section content
  * design merge margin logic (like for admonition block)
  