Create a class method that returns a proc needed for parameter filtering

@ggrossman @rtatsumi @grosser @steved555 @morten @craiglittle 

This created a class method that returns a proc that can be used in a Rails application to redact credit card numbers from logs. Ex:

```
Rails.application.config.filter_parameters.concat CreditCardSanitizer.parameter_filter
```
:heart: