Creates a Leipzig.js glossing object
@constructor
@param {String|NodeList|Element} selector - determines elements to be glossed
@param {Object} config - configuration object
function(selector, config = {}) {
  if (!(this instanceof Leipzig)) {
    return new Leipzig(selector, config);
  }

  if (typeof selector !== 'undefined') {
    if (typeof selector === 'string' ||
        selector instanceof NodeList ||
        selector instanceof Element) {
      config.selector = selector;
    } else if (typeof selector === 'object') {
      // if the first argument is an object, let's assume it's actually a
      // configuration object, and not the selector
      config = selector;
    } else {
      throw new Error('Invalid selector');
    }
  }

  this.config(config);
}