Implemented unit tests for strict and valid CNPJ and CPF

These unit tests were missing, thus reducing the code coverage.
Minor fix in the NuGet package
Updated NuGet to version 2.7.1
Implemented CEP validation.

This is a brand new implementation for CEP validation only.
Implemented unit tests for empty strings in CPF and CNPJ validation.
Changed version to 0.2.2
Included documentation for Cep class
Updated NuGet spec file
Updated version to alpha release
Fixed the documentation file's extension
Fixed CEP validation when it is incomplete
Fixed the regular expression for CEP with more than eight characters.
Implemented unit tests for CNPJ greater than 14 characters and CPF greater than 11 characters.
Implemented StyleCop and refactored the code to follow StyleCop rules.
Updated README file.
Implemented validation for CPF with repeating digits.