utilize »EMOJIone« for website

No matter if a emoji is given by the UTF-8 character or the shortname
via `:shortname:` EMOJIone's JavaScript method `toImage` [1]
> convert native unicode emoji and shortnames directly to images
so each looks similar to GitHub's markdown rendered version.

[1] https://demos.emojione.com/3.1/jstoimage.html

style.css

@@ -55,6 +55,8 @@ sub { bottom: -0.25em; }
 /** Remove border when inside `a` element in IE 8/9/10. */
 img { border: 0; }
 
+img.emojione { height: 20px; }
+
 /** Correct overflow not hidden in IE 9/10/11. */
 svg:not(:root) { overflow: hidden; }