Options to specify tag and registering of JavaScript

Allow the specifying of the container tag, defaults to `<div/>`.
Optional registering of Pjax events against the link and form selectors.

I needed to use Pjax in a table so the option to specify the container as a `<tbody/>` was needed.
I'm also using `$.pjax.reload(...)` so the JavaScript the widget registered wasn't needed.
This enhancement should be documented (in `options` comment).