code: function safeStep(callback, stepFn) {
      var err;
      try {
          stepFn();
      }
      catch (error) {
          err = error;
      }
      callback(err);
  }
docs: Runs `stepFn`, catching any error and passing it to `callback` (Node-style).
  Otherwise, calls `callback` with no arguments on success.
  
  @param {function()} callback
  @param {function()} stepFn