Update functions completion with arguments

These completions auto generate based on http://www.autoitscript.com/autoit3/docs/functions.htm

"string argument"
[optional argument]
![function-completions](https://f.cloud.github.com/assets/3766193/1785165/83d3eb1c-68df-11e3-9ef0-e72ed15a52a2.png)