anchor.diff:  * allow color and string template to be specified for alt text (#730)
   * if image fails to load, could draw a box with an X in it to indicate it's broken
   * enable fit=scale-down (or fit=contain) for title logo image; otherwise, just let it get clipped (will require passing at option to embed_image to prevent page from advancing)
  +* add option to force margin (to apply even when at top of page)
   * make section depth for section-title attribute in running content configurable (#726)
   * add ability to set watermark_image which goes on top of each (non-imported) page instead of bottom (#727)
   * AsciiDoc table cell leaves padding below last block (due to no margin collapsing)
  
positive.code:  ** 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)
   ** consider having a fallback for prose and fallback for literal
  * should we drop "<font>" handler in formatted text transform?
  * FILE ISSUE: ttfunk 1.5.0 chokes on narrow no-break space char \u202f
  * implement text transform for running content (#702)
  * implement start line number in source listing (rouge) (#752)
   ** shouldn't this be fixed in core at the same time? (core #1742)
  
negative.code: == Prawn Wishlist
  
  * fragment should be able to specify it's own width
  * test string with include? before gsub (for example, stripping zero-width spaces)
  
  == Known Issues
  
  