Add subscribing account balance changes support for BTCChina streaming service.

[WEBSOCKET API V1.2.1](http://btcchina.org/websocket-api-market-data-documentation-en#websocket_api_v121): 2014-09-30 Websocket API v1.2.1 Added 'account_info', added Java sample code for 'account_info' method and Ruby sample code for 'order' and 'account_info' methods.