#132 support for screen Transparency on WIN/OSX/Linux

will also need following pull requests:
https://github.com/rogerwang/blink/pull/7
https://github.com/rogerwang/chromium.src/pull/27

I've added SetTransparent function in javascript's window class
you can also set it in package.json file, add "transparent": true inside "window"

<b>OSX screenshot (Transparent window with frame) :</b>
![screen shot 2014-10-15 at 12 31 31 pm](https://cloud.githubusercontent.com/assets/4043527/4640581/39d41eb6-5424-11e4-9b0a-563fb7dea89a.png)

<b>WIN8 screenshot (Transparent window without frame, with toolbar) :</b>
![screen shot 2014-10-15 at 12 37 46 pm](https://cloud.githubusercontent.com/assets/4043527/4640633/3514b358-5425-11e4-9667-5e2113c2da0a.png)

@rogerwang I'm investigating it now