Address class assumes too much about the structure of email addresses

[fs]

Currently there is a tight validity check in place in turbomail.util.py.

This regex is imho too strict as it prevents the use of internationalized domain names (see #69). Furthermore it forbids email addresses like 'foo@…' which may be perfectly valid. IMHO the validation must allow internationalized domain names and it should be at least configurable to accept addresses which do not contain a top-level domain.

[amcgregor]

Corrected in r112: foo@corporation, foo@domain.com.au, and internationalized domains are now accepted.