function clean (node) {
      for (var n = 0; n < node.childNodes.length; ++n) {
        var child = node.childNodes[n];
        if (child.nodeType === 3) {
          if (!/\S/.test(child.nodeValue)) {
            node.removeChild(child);
            --n;
          } else {
            child.nodeValue = child.nodeValue.split('\n').join(' ');
            child.nodeValue = child.nodeValue.replace(/(\s)+/g, '$1');
          }
        } else if (child.nodeType === 1) {
          clean(child);
        }
      }
    }
Converts an HTML string into a markdown string
@param src
@returns {string}