Hyphens in domain label

[devikasondhi]

Hello,

According to RFC 1035, domain label cannot start or end in hyphen. Validation on email addresses such as email("andy-noble@data-workshop.-com") should throw a ValidationFailure while the function currently returns True.

[devikasondhi]

Here is another inconsistency with the specs.:
Email can't end with a dot: "andy.noble@data-workshop.com." should be flagged as invalid email

[kvesteri]

PRs welcome