Add RFC822 specification for validating an email address.
user
```ruby
# encoding: binary
#
# RFC822 Email Address Regex
# --------------------------
# 
# Originally written by Cal Henderson
# c.f. http://iamcal.com/publish/articles/php/parsing_email/
#
# Translated to Ruby by Tim Fletcher, with changes suggested by Dan Kubb.
#
# Licensed under a Creative Commons Attribution-ShareAlike 2.5 License
# http://creativecommons.org/licenses/by-sa/2.5/
# 
# Source: http://tfletcher.com/lib/rfc822.rb
# RFC822: http://www.w3.org/Protocols/rfc822/#z8

module ActiveESP
  module RFC822
    EmailAddress = begin
      qtext = '[^\\x0d\\x22\\x5c\\x80-\\xff]'
      dtext = '[^\\x0d\\x5b-\\x5d\\x80-\\xff]'
      atom = '[^\\x00-\\x20\\x22\\x28\\x29\\x2c\\x2e\\x3a-' +
        '\\x3c\\x3e\\x40\\x5b-\\x5d\\x7f-\\xff]+'
      quoted_pair = '\\x5c[\\x00-\\x7f]'
      domain_literal = "\\x5b(?:#{dtext}|#{quoted_pair})*\\x5d"
      quoted_string = "\\x22(?:#{qtext}|#{quoted_pair})*\\x22"
      domain_ref = atom
      sub_domain = "(?:#{domain_ref}|#{domain_literal})"
      word = "(?:#{atom}|#{quoted_string})"
      domain = "#{sub_domain}(?:\\x2e#{sub_domain})*"
      local_part = "#{word}(?:\\x2e#{word})*"
      addr_spec = "#{local_part}\\x40#{domain}"
      pattern = /\A#{addr_spec}\z/
    end
  end
end```
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