Adding IE8 Support

Support IE8 required a couple of minor changes:

* Using `window.attachEvent` if `window.addEventListener` doesn't exist.
* The usage of the `:not` selector in autoinit, so I replaced that with a check for if the `data-pym-auto-initialized` attr has been set when iterating over each element that matches `[data-pym-src]`.

The examples should all work in IE8 except the one that use D3.