Add a "strict" validation ?

[georgeyk]

Consider the code 0000098795147 (taken from test_valid_gtin8_string_with_leading_zeros test), it is a valid gtin8 code, but should not be considered a valid gtin13 code.

The list of prefixes https://www.gs1.org/company-prefix. Maybe there are other prefixes than 00000 that should be validated depending on gtin "type".

Another case to consider, invalidate 00000000 (it's a valid code, but I think it's reserved or similar). So, maybe we should have a way to make the validation more "restricted". Any thoughts ?

[charithe]

Sounds like a useful feature. I will be happy to accept a PR.