JS: Add Currency.json_rewrite().
JS: Add Currency.json_rewrite().

wilsonianb/ripple-lib,wilsonianb/ripple-lib,ripple/ripple-lib,darkdarkdragon/ripple-lib,ripple/ripple-lib,wilsonianb/ripple-lib,ripple/ripple-lib,darkdarkdragon/ripple-lib,ripple/ripple-lib,darkdarkdragon/ripple-lib