Improve email validation (Issue #1)

Should follow the RFC 5322
(http://tools.ietf.org/html/rfc5322#section-3.4)

Return true for:
"John Doe" <john.doe@example.com>
John <john.doe@example.com>
<john.doe@example.com>
john.doe@example.com

Return false for:
John Doe <john.doe@example.com>
john.doe.@example.com
john.doe@example.com>
<john.doe@example.com
"John <john.doe@example.com>