Converts an array of number values to array of differences between each pairs of values
for example : [100, 101, 102, 103, 104, 105] => [100, 1, 1, 1, 1, 1]
@param {array<number>}
@return {array<number>}
function(numArray) {
    numArray.sort(function (a, b) {  return a - b;  });
    for (var i=0, prev=0, diff=0, result=[], len=numArray.length; i<len; i++) {
      diff = numArray[i] - prev;
      prev = numArray[i];
      result.push(diff);
    }
    return result;
  }