Added support for '&' when verifying valid ASN.1 printable string value

[JoaquinRuiz7]

Hi sir, great library!

I was having some trouble while checking for the certificate status when string values contained the "&" character.
Exploring the code I bumped into that regex that excludes the character in question, I added "&" to the regex validation.

Works great!

Have a nice day!

[mlocati]

The standard does not include the & character: see https://www.itu.int/rec/T-REC-X.680-202102-I/en and in particular page 87 of the PDF you can download from that page, where we have:

It's also mentioned in Wikipedia:

The PrintableString definition does not include the at sign (@) or ampersand (&). This sometimes causes problems for naive implementers who attempt to put an SMTP email address into an X.509 digital certificate Distinguished Name.

[JoaquinRuiz7]

Great, thanks for he info. Im closing this pull request then.