Allow filtering params based on parent keys

Some parameters on APIs have ambiguous names
that cannot be filtered altogether.

For example, it makes sense not to filter :code in

    { file: { code: '<% source %>' }}

It makes sense however to filter it in

    { credit_card: { code: '424242424242' }}

This PR allows doing so by using 

`config.filter_parameters += ["credit_card.code"]`