Updated the Arduino + ChromeExtension Example

[kunalghosh]

Hi Renaun,

I was using your example to learn interfacing Chrome extensions to Arduino sketches and made a bunch of changes to update the extension to work with the latest Chrome Serial API.

I have also made a small addition to the blink.js script to keep looking for serial connections in case the extension is launched before the arduino is plugged into the computer. Faced this issue a couple of times, thought I'd fix it :)

This pull request includes all the javascript changes as well as the changes to the Read-me file.

Kunal