Create sniff for tag declaration validation

[aik099]

For every tag method (method name starts with capital letter and 1st parameter is called $params, class name has TagProcessor) we need to:

1. validate, that method scope is protected (empty scope considered public)
2. validate, that $params parameter type hint is array
3. analyze method DocBlock (if present) to:
   • have @return string
   • the $params parameter declaration to be @param array $params Tag params.