static fromDateTimes(start, end) {
    const builtStart = friendlyDateTime(start),
      builtEnd = friendlyDateTime(end);

    const validateError = validateStartEnd(builtStart, builtEnd);

    if (validateError == null) {
      return new Interval({
        start: builtStart,
        end: builtEnd,
      });
    } else {
      return validateError;
    }
  }
Create an Interval from a start DateTime and an end DateTime. Inclusive of the start but not the end.
@param {DateTime|Date|Object} start
@param {DateTime|Date|Object} end
@return {Interval}