Merge pull request #625 from nimrood/develop

fix for issue#623 - Exception caused when only 1 CurrencyPair is provided
Implement BTCChina Trade API v2.0.1: Added two more parameters for getTransactions API method: "since" and "sincetype".
Implement BTCChina Data API v1.3.1: Added two more return values "vwap" and "prev_close" for ticker API.
Merge pull request #626 from sutra/develop

Implement BTCChina Trade API v2.0.1: Added two more parameters for getTransactions API method: "since" and "sincetype".
Merge pull request #627 from sutra/Data_API_v1.3.1

Implement BTCChina Data API v1.3.1: Added two more return values "vwap" and "prev_close" for ticker API.