Docs: Update the `Track JS errors in GA` section

Add column number parameter to the example to reflect the recent changes
in the specification and in the Chrome and IE 10 implementations.

http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html#errorevent
https://code.google.com/p/chromium/issues/detail?id=264197

Close #1417.
Compress .png files losslessly.

Use zopfli-png with 1000 iterations, pngout /r with various blocksizes and deflopt.

The total difference is -320 bytes.