use requests for MarketData and enable HTTP streaming
convert TradeAPI to use requests
Inherit TradeAPI from MarketData and reuse the same HTTP connection
Add methods for futures API
Added futures ticker
get_future_info: Fix spacing breaking the function using requests
Clean up TickerAPI and support okcoin.com currency pairs
Merge pull request #3 from shanew/master

Added futures, enable http keepalive by switching to requests