docs: function Simulator() {
          this.time = 0;
          this.method = new ExplicitEuler();;
          this.handlers = new Array();
          this.entities = new Array();
          this.initTime = 0;
          this.maxTime = 1;
          this.timeStep = 1;
          // override default attributes or methods
          for(var n in arguments[0]) {
              this[n] = arguments[0][n];
          }
      }