Support the new extra letter at the end of PPS numbers (weight=9), while maintaining compatibility with the old format.
Add a few test PPS numbers, keep ie coverage at 100%.

References:

• https://www.welfare.ie/en/Pages/PPSN.aspx
• http://www.citizensinformation.ie/en/social_welfare/irish_social_welfare_system/personal_public_service_number.html

Owner

Thanks for your change. I've merged your change with a few minor changes in a4012f5.

I've included a few minor PEP8 fixes and made the calc_check_digit() function a little cleaner.

The Brin (Basis Registratie Instellingen) is a number to identify
schools and related institutions.

Addresses trac ticket #6.

Improve for: Issue arthurdejong#6: Custom text not allowed under barcode.

Fixes arthurdejong#6