ctp: add testmd.py module

Test to Market Data Map.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>
ctp:ctpagent/ctpapi/mdmap/testctp: update

1) ctpagent: update OnRtnDepthMarketData().
2) ctpapi: update OnRtnDepthMarketData() and revmoe market_data2tick().
3) mdmap: fix using same object instance out dict map.
4) update testctp.py.

Signed-off-by: Zhengwang Ruan <ruan.zhengwang@gmail.com>