Remove redundant println
Change url of BTCChina API

Both data.btcchina.com and api.btcchina.com are accessible, but if you use any private API (get account information or trade) with data.btcchina.com, it returns JSON with a PHP warning (WTF). api.btcchina.com is free from this problem and it is officially defined in http://btcchina.org/api-trade-documentation-en
Fix result value of cancelOrder, buyOrder, sellOrder of BTCChina

These methods were not correctly implemented or the documentation has changed
Remove trailing zeros and truncate precision of amount in buyOrder and sellOrder of BTCChina

Due to the implementation of BTCChina’s server, if you have any trailing zeros in amount value or number of digits of fractional part are greater than 3, server will return 401 Unauthorized because the hash signature differs.
Merge pull request #256 from BYVoid/develop

Bug fixes on BTCChina