[VALIDATION] Request::QueryStringParameterValidator

[nmacherey]

Validator for query string parameters

[remy-theroux]

Hi, i'd like to help to extend request validation to query parameters (path, headers...). But i am not sure how to do in the spirit of the library. Do i have to had another ContentValidator which should be named QueryParametersValidator. If yes, validateRequest interface method should use ServerRequestInterface instead of RequestInterface as it hasn't parameters getters (like getQueryParams).
Can you help me understand your lib please as i could contribute to it. Great job by the way