code: function nextJob(index, callback) {
              if (typeof (index) === 'function') {
                  callback = index;
                  index = 0;
              }
  
              if (queued_jobs.length === 0) {
                  return callback(null, null);
              }
  
              var slice = queued_jobs.slice(index, index + 1);
  
              if (slice.length === 0) {
                  return callback(null, null);
              } else {
                  return getJob(slice[0], callback);
              }
          }
docs: Get the next queued job. index - Integer, optional. When given, it'll get the job at index position (when not given, it'll return the job at position zero). callback - f(err, job)