Add VAT modulus11 check for countries

[gemal]

some countries has a modulus 11 check build into the number The VAT validator should be able to check that

[gemal]

Do you accept pull requests?

[gemal]

@dannyvankooten would you accept pull request for this?

[dannyvankooten]

Hey @gemal,

Yes, definitely! Anything that could invalidate VAT numbers before sending a request off to the (sometimes somewhat unreliable) VIES API is encouraged, in my book. :+1:

Do you have a source on which countries have such a format? GB, from the looks of it?

[gemal]

possible code could be used from here: https://gist.github.com/svschannak/e79892f4fbc56df15bdb5496d0e67b85