To-Do:

Export to ePub
Export to PDF
Redesign thx for support page
Move support info (like: bank account, PayPal email and Zarrin Card) to config and show them if something exists.
Beautify the NEXT and PREVIOUS chapter

Usage:

Each article should have this header:

---
layout: article
chapter: "the name of current chapter"
order: "article number in book index"
title: "the name of article"
---

Here's an example:

---
layout: article
chapter: اصول و مقدمات
order: 1
title: فلسفه آزادی نرم‌افزار
---