* @summary Substract the specified number of business days (mon - fri) to the given date.
*
* @description
* Substract the specified number of business days (mon - fri) to the given date, ignoring weekends.
*
* @param {Date|Number} date - the date to be changed
* @param {Number} amount - the amount of business days to be subtracted. Positive decimals will be rounded using `Math.floor`, decimals less than zero will be rounded using `Math.ceil`.
* @returns {Date} the new date with the business days subtracted
* @throws {TypeError} 2 arguments required
*
* @example
* // Substract 10 business days from 1 September 2014: