code: function(filepath, index) {
          index = index || 1;
          var params = this.get_path_info(filepath);
          params.index = index;
          var newpath = Handlebars.compile(this.config.sequential_template)(params);
          return (fs.existsSync(newpath)) ? this.get_sequential_filepath(filepath, index + 1) : newpath;
      }
docs: Returns the next available sequential filename for a given conflicting filepath
  @param  {String} filepath
  @return {String}