Include postal code example

[Etroid]

Problem/Motivation

There are many scenarios in which the postal code validation return ambiguous error messages. It might be useful to provide some additional context through a valid example. Google provides a list of valid postal code examples under the zipex property. As a first step to improve postal code validation, we would need to include this property in the addressing resources.

• [ ] Updated generate_address_data.php to include zipex on both country and subdivision level
• [ ] Added property postalCodeExample and getter to AddressFormat class

Closes #127

[bojanz]

This is a good idea. However, it looks incomplete. The generate script also creates a postal_code_example for subdivisions, but the subdivision json files weren't updated, and neither was Subdivision.php

[Etroid]

Included subdivisions resources and added postal_code_example to both AddressFormat and SubDivision