code: function register(types, converter) {
    types.split(' ').forEach(function (type) {
      converters[type] = converter;
    });
  }
docs: Register a converter.
  
  Takes a string, splits by spaces (in case a given markup can
  have multiple extensions), and maps the method in the available
  converters list.
  
  @param {string} types - The markup types (extensions).
  @param {function(string, object)} converter - Markup converter.