* Add overview to payment data store docs
* Add documentation for isExpressPaymentMethodActive
* Add documentation for getActiveSavedToken
* Remove _ from Example heading
* Add documentation for getActivePaymentMethod
* Add documentation for getAvailablePaymentMethods
* Add documentation for getAvailableExpressPaymentMethods
* Add documentation for getPaymentMethodData
* Add documentation for getSavedPaymentMethods
* Add documentation for getActiveSavedPaymentMethods
* Add documentation for shouldSavePaymentMethod
* Add documentation for getCurrentStatus
* Change docs for shouldSavePaymentMethod to getShouldSavePaymentMethod
* Add documentation for normal/express paymentMethodsInitialized
* Add table of contents for payment method documentation