lib/schedule.js
function Range(start, end, step) {
  this.start = start || 0;
  this.end = end || 60;
  this.step = step || 1;
}
function Range(start, end, step) {
  this.start = start || 0;
  this.end = end || 60;
  this.step = step || 1;
}
/* Range object