Previously, no splitting would occur if the paragraph count exceeded the
desired number of pages by one.

Fixes #1

Also replaces a `continue` with what was likely meant to be a `break`, which
hopefully will fix #10 and #11.

Build on work by @bendoh merged in f96afe53 and implement two paging options as toggles in the UI. Also makes the approach to applying the various paging types more modular and a bit easier to follow.

Lastly, WP coding standards. There's lots to clean up, so I only dealt with those bits I actually touched in the aforementioned work.

specifying page count

Add settings field for post types to Reading page and update filter used to populate post types class variable to use same. Fixes #1.

Started adding control over number of pages a post is broken over. Will return to this as it requires rewriting how post content is filtered. See #2.

Basic autopaging functionality. Splits over two pages, includes an option to disable. Filter exists to modify supported post types.