function shift(strnum, exponent) {
    if (typeof strnum === 'number') {
      strnum = '' + strnum;
    }

    var parsed = parse(strnum);
    if (parsed === null) {
      return strnum;
    } else {
      return format(shiftParts(parsed, exponent));
    }
  }
Shift the exponent of the given number (as a string) by the given amount.

  shift('12', 2);  // '1200'
  shift('12', -2); // '0.12'

@param {string|number} strnum
@param {number} exponent
@return {string}