Add an optional features

[e8johan]

Add a new filter function to the options that let's you filter the pages, to be able to remove pages that only apply to the web site and not the PDF export.

Added a TOC function, rendering an optional TOC before the rendered pages.

Added the ability to inject a front page (or front pages) before the TOC.

(sorry for mixing multiple features, my fork is moving forward due to project needs)