Prevents re-rendering if the page doesn't change

Also prevents from "going off the edge", that is, setting the page to a
number < 1 or > total_pages.
Adds a change method

The change method allows a pager to have its page changed via JS. This
is useful when you have multiple pagers on a page and want to keep them
in sync. The callback, if supplied, is not called when change is
invoked.
Adds option to disable turbolinks

Turbolinks are on by default in rails4, but they are incompatible with
these sorts of pagination links. For more information see
https://github.com/rails/turbolinks/

This option is disabled by default.