docs: function save_config(path, config) {
  	debug.assert(path).is('string');
  	debug.assert(config).is('object');
  	return $Q.fcall(function stringify_json() {
  		return JSON.stringify(config, null, 2);
  	}).then(function write_to_file(data) {
  		return FS.writeFile(path, data, {'encoding':'utf8'});
  	});
  }