code: function pipe(opts, cb) {
    if (typeof opts === 'function') {
      cb = opts;
      opts = {};
    }
  
    if (!cb) {
      cb = function () { }
    }
  
    opts = opts || {};
  
    var results = validate(opts);
  
    if (!hasErrors(results)) {
      return cb();
    }
  
    var err = new Error('Unable to validate dependencies');
    err.meta = results;
    return cb(err);
  }
docs: Callback style interface to #validate.
  
  @param opts an options Object (see README.md).
  @param cb a callback to pass a potential error to.