Add auto code completion (without press Ctrl+Space manually)

- Add auto code completion (without press Ctrl+Space manually)
- Support use tab key to accept code completion option
- Add Code Complete Delay in Editor Setting
![](http://oi62.tinypic.com/izuiw9.jpg)

check http://www.godotengine.org/forum/viewtopic.php?f=8&t=546#p2289 for more info