Allow to configure validator with custom authentication result codes and validation messages

[Xerkus]

This PR adds feature to configure Authentication validator with user defined authentication result codes and their corresponding validation messages.
Solves #41

• Are you creating a new feature?
  • Why is the new feature needed? What purpose does it serve?
    Authentication Result allows custom result codes to be specified but Authentication validator does not provide a way to map those codes to meaningful validation error messages. This feature fixes that by introducing new configuration option for Authentication validator.
  • How will users use the new feature?
    New constructor configuration option code_map added. It is an array of [int $resultCode => string $validatorMessageKey].
    Custom validator message key can be specified which is then registered as a new template that can be modified using common ways provided by Zend\Validator\AbstractValidator: setMessage() method or messages option.
  • Base your feature on the develop branch, and submit against that branch.
  • Add only one feature per pull request; split multiple features over multiple pull requests
  • Add tests for the new feature.
  • Add documentation for the new feature.
  • Add a CHANGELOG.md entry for the new feature.

[weierophinney]

Code looks good.

I've flagged a couple documentation changes, and have one question about code types.

[Xerkus]

@weierophinney I pushed improved documentation for validator that I hope should be more clear.

[weierophinney]

This reads REALLY well, and makes it very clear how everything works!

I've provided a number of suggestions that fix grammar and/or punctuation. You should be able to commit each and/or batch them from the UI (instead of addressing them one-by-one manually).