Custom marked renderer for gist code quotes

gistfile1.js

var r = new marked.Renderer()
var oldCode = r.code;
r.code = function(code, lang) {
  if (lang === "gist") {
    return '<code gist="https://gist.github.com/' + code + '.json"></code>';
  } else {
    return oldCode(code, lang);
  }
}