 Feature Request - Addd masking option to selectively mask specific properties by the masking operators

While using this library we've stumbled upon a use-case were we want to include **only specific** properties to be handled by the masking operators, and not automatically be masked by the _MaskProperties_ option. 

The _ExcludePropeties_ can't be used in our case as the properties may vary and we can't control/enforce which one are being added / used.
