Add support for serial numbers under "markings"
In the "markings" element, I suggest that we add support for serial numbers. This can be done by adding four tags:
serial_number, boolean (true/false)
serial_number_format, string, expressed as a "regular expression" but needs to have x amount of digits in it.
serial_number_start, integer, the number to start from. Will have to replace the digits from the "serial_number_format" above.
serial_number_increase_by, integer, the increase in number from "serial_number_start" with each product.