Payum/Payum — pull request #137 by makasim (2014-05-28 15:04:17+00:00)
Title: [security] add mask util. allows mask strings with diff options.

The idea is taken from the [Matt comment's](http://brett.batie.com/software-development/post-about-format-credit-card-with-xs-and-dashes-using-php/).

Util produce next results:

````
“3456-7890-1234-5678″ = “3XXX-XXXX-XXXX-5678″
“4567890123456789″ = “4XXXXXXXXXXX6789″
“4928-abcd9012-3456″ = “4XXX-XXXXXXXX-3456″
“498291842″ = “4XXXX1842″
```

You can configure mask symbol and last show chars number.

/cc @pjedrzejewski