code: function KeyboardController(upKey, downKey) {
      var myHandle,
          direction = 0,
          handleKeyDown = function (e) {
              if (e.which === upKey) {
                  direction = settings.keyboardControllerSpeed;
              } else if (e.which === downKey) {
                  direction = -settings.keyboardControllerSpeed;
              }
          },
          handleKeyUp = function (e) {
              if (e.which === upKey || e.which === downKey) {
                  direction = 0;
              }
          };
  
      this.mount = function (handle) {
          myHandle = handle;
          document.addEventListener('keydown', handleKeyDown);
          document.addEventListener('keyup', handleKeyUp);
      };
      this.dismount = function () {
          document.removeEventListener('keydown', handleKeyDown);
          document.removeEventListener('keyup', handleKeyUp);
          myHandle = null;
      };
      this.step = function () {
          if (direction) {
              myHandle.move(direction);
          }
      };
  }
docs: /* export 
  Controls a handle from the keyboard