anchor.diff:  == 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
   
  
positive.code: * 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)
  * 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)
  
negative.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
  * transform table cell text inside correct font context (allows us to check the current font, such as in breakable_uri)
  * should we drop "<font>" handler in formatted text transform?
  * ttfunk 1.5.0 chokes on narrow no-break space char \u202f (patch applied; https://github.com/prawnpdf/ttfunk/issues/39)
  * 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)
  