[Mod]import rqdatac only if required

docs/cta_strategy.md

@@ -0,0 +1 @@
+# Introduction

docs/index.md

@@ -1,6 +1,7 @@
 # vn.py文档
 
 
-* [Introduction](introduction.md)
-* [Install](install.md)
-* [Quick Start](quickstart.md)
+* [vn.py简介](introduction.md)
+* [项目安装](install.md)
+* [基本使用](quickstart.md)
+* [CTA策略模块](cta_strategy.md)

docs/quickstart.md

@@ -0,0 +1 @@
+# Introduction

vnpy/app/cta_strategy/engine.py

@@ -11,8 +11,6 @@ from threading import Thread
 from queue import Queue
 from copy import copy
 
-import rqdatac
-
 from vnpy.event import Event, EventEngine
 from vnpy.trader.engine import BaseEngine, MainEngine
 from vnpy.trader.object import (
@@ -105,6 +103,8 @@ class CtaEngine(BaseEngine):
         if not username or not password:
             return
 
+        import rqdatac
+        
         self.rq_client = rqdatac
         self.rq_client.init(username, password,
                             ('rqdatad-pro.ricequant.com', 16011))