Camera example with edge detection

Resubmitting pull-request #32 to the `develop` branch with the following modifications:

 * No longer rewriting browser globals like `window.URL` and `navigator.getUserMedia`.
 * Fixed undeclared `error` in error callback for `getUserMedia`
 * Wait for `canplay` video event to start Seriously rendering to avoid render warnings

**Note:** In the `develop` branch the video is no longer rendering to the canvas in FireFox. However, it's also not working in the main example so it seems like there is something in progress elsewhere that is causing this. I dropped the exact same code into the master branch and it works fine in FireFox.