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

[munitss]

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.