Changes to plugin break CSS styling for pagination

Comparing v1.3.1 to v1.2.4, the css for the pagination links breaks due to the lack of classes. In v1.2.4 paginate_links added pip-nav-prev and pip-nav-next to the li elements. This is not the same behavior in v.1.3.1, making it difficult to properly style the links.

Also, as a matter of code cleanup, it seems that in v.1.3.1 for the paginate_links method, the $page and $per_page variables are unused and should be removed.