Add IBAN class

[RemyDuijkeren]

A IBAN number is used for Money and has a lot of logic to it. Maybe it's interesting to add an IBAN class to this library? Or is it to much out of scope for this library?

See http://en.wikipedia.org/wiki/International_Bank_Account_Number

[rubenrorije]

I created an IBAN class already here. Also there is a CreditCard class that might be useful.
I am happy to move them over here. I have to make some changes to make them fit the contributing guidelines, but that is no problem for me.