Support async somehow

[yamadapc]

There's probably a way to support async calls, with a clean API. Something like:

/**
 * @example
 *     something('here', cb)
 *     // async => Error('Yields an error with "here"')
 *     something('there', cb)
 *     // async => 'result'
 */

function something(arg, cb) {
  if(arg === 'here') {
    cb(new Error('Yields an error with "here"');
  }
  else {
    cb(null, 'result');
  }
}