anchor.diff:  * scale SVG background image to fit page in the same way raster image is scaled (#765)
   * allow page background size to be controlled using image macro attributes (#1117)
   * allow page background image position to be controlled using position attribute on image macro (#1124)
  -* add support for fit=cover for cover, page background, and running content images (#1136)
  +* add support for `fit=cover` for cover, page background, and running content images (#1136)
   * change default background image position to center (#1124)
   * allow cover image position to be controlled using position attribute on image macro (#1134)
   * change default cover image position to center (#1134)
   * allow cover image size to be controlled using fit, pdfwidth, and width attributes; don't scale image by default (#1134)
  -* set enable_file_requests_with_root and enable_web_requests options for all SVGs (#683)
  -* automatically set pdf-stylesdir if pdf-style ends with .yml and pdf-stylesdir is not specified (#1126)
  +* set `enable_file_requests_with_root` and `enable_web_requests` options for all SVGs (#683)
  +* automatically set `pdf-stylesdir` if `pdf-style` ends with .yml and `pdf-stylesdir` is not specified (#1126)
   * replace hyphens with underscores in top-level theme keys
   * allow hyphens to be used in variable references in theme (#1122)
   * allow theme to control background and border of inline code (literal) (#306)
  
positive.code: * add visual regression capability to test suite (@beatchristen)
  * ensure index section doesn't get numbered when using Asciidoctor < 1.5.7
  * add part signifier and part number to part title if partnums is set; allow signifier to be customized using part-signifier attribute (#597)
  * add support for the chapter-signifier attribute as the prefered alternative to chapter-label
  * warn if the image referenced in the running content cannot be found (#731)
  
  == 1.5.0.alpha.17 (2019-04-23) - @mojavelinux
  
negative.code: * allow admonition icon image to be remote (if allow-uri-read is set) or data URI (#1711)
  * allow theme to configure font color of unresolved footnote using unresolved role
  * show textual label on admonition if icon image fails to embed (#1741)
  * allow theme to disable title page by assigning false to `title-page` category key (#1754)
  * allow Rouge theme to be specified as theme class or instance (API only)
  * allow theme to control font size of dot leader in TOC
  * allow section to override `outlinelevels` for self and children using `outlinelevels` attribute on section
  * use value of `author` attribute for PDF info and pdfmark if locked by the API (#1778)
  * only extend theme in extends hierarchy once unless modified with `!important` (#1800)
  * add print-optimized themes (`default-for-print` and `default-for-print-with-fallback-font`) (#1699)
  * add support for power operator in theme (with same precedence as multiply and divide) (#1813)
  * include floor and ceil match characters in fallback font (#1832) (*@oddhack*)
  * allow horizontal and vertical lines of table grid to be styled independently (#1875) (*@hextremist*)
  