code: function type(filename, opts) {
    opts = opts || {};
    if (opts.parse && typeof opts.parse === 'string') {
      return opts.parse;
    }
    var ext = path.extname(filename);
    return ext || 'json';
  }
docs: Detect the type to parse, JSON or YAML. Sometimes this is based on file extension,
  other times it must be specified on the options.
  
  @param  {String} `filename`
  @param  {Object} `opts` If `filename` does not have an extension, specify the type on the `parse` option.
  @return {String} The type to parse.