Add Paypal Finance IDs

[freddyheppell]

Various forms of PayPal URLs found in the wild, with unique identifiers:

1. https://www.paypal.com/donate/?hosted_button_id=ABC123
2. http://paypal.me/ExampleUsername, https://www.paypal.com/paypalme/ExampleUsername
3. https://www.paypal.com/cgi-bin/webscr?cmd=_subscr-find&alias=someaddress%40example%2ecom
4. https://www.paypal.com/cgi-bin/webscr?cmd=_donations&business=someaddress%40example.com&item_name=Some+Donation+Name&currency_code=USD&source=url
5. https://www.paypal.com/donate?business=ABC123&item_name=Some+Donation+Name&currency_code=CAD
6. https://www.paypal.com/cgi-bin/webscr?cmd=_s-xclick&hosted_button_id=ABC123

All the ABC123 IDs seem to be 13 chars [A-Z0-9] but I don't know that this is always true for sure. URLs with the webscr and a hosted_button_id may be donations or shopping cart-style purchases.