Moved the Public Suffix List code into its own library

[ekscrypto]

I realize that there are other uses for the Public Suffix lookup, including HTTP servers, proxy servers, etc. So I moved it into it's own library over at https://github.com/ekscrypto/SwiftPublicSuffixList

I've also updated the EmailSyntaxValidator to use a closure for validating the domain instead of the Public Suffix Rules, so if additional validation is needed it can be done. Like ... doing a DNS query for MX records for the domain -- it's possible now. Or doing no validation whatsoever... also possible.

These changes will be published as part of the next release... 1.0.0. Stay tuned!