Feature/Configurable default validation type, #48

[bestwebua]

Implement configurable default validation type.

You can predefine default validation type for Truemail.validate('email@email.com') call without with-parameter. Available validation types: :regex, :mx, :smtp. By default validation type still be :smtp

Truemail.configure do |config|
  config.verifier_email = 'verifier@example.com'
  config.default_validation_type = :mx
end

• Added configurable default validation type option, [FEATURE] Opt out of SMTP validation #48
• Updated tests
• Updated documentation
• Updated wiki
• Updated gem version