##<gold-cc-input>
gold-cc-input is a single-line text field with Material Design styling
for entering a credit card number. As the user types, the number will be
formatted by adding a space every 4 digits.
<gold-cc-input></gold-cc-input>
It may include an optional label, which by default is "Card number".
<gold-cc-input label="CC"></gold-cc-input>
Validation
The input can detect whether a credit card number is valid, and the type
of credit card it is, using the Luhn checksum. See http://jquerycreditcardvalidator.com/
for more information.
The input can be automatically validated as the user is typing by using
the auto-validate and required attributes. For manual validation, the
element also has a validate() method, which returns the validity of the
input as well sets any appropriate error messages and styles.
See Polymer.PaperInputBehavior for more API docs.
Styling
See Polymer.PaperInputContainer for a list of custom properties used to
style this element.