Move site to new engine

* Move our site from our own Jinja2+Markdown to Pelican
* Move all pages from Markdown to RST(-highlightJS,+Pygmentize)
* Create plugin for documentation building (HTML for DocBook based and RST for hand-written texts)
  - Supports HTML for DocBook-generated documentation
  - Supports RST for HandWrittend Texts
  - Embedding into Pre-Based Templates
  - Using BeautifulSoup library for generating proper titles
* Adding Header to all site pages (e.g. Documentation)
* Modifications of CSS (we need to bring order to our CSS's)
* Modifications for DocBook xslt files and generations
* Add GitHub Ribbon
* Move FAQ to Documentation
* Documentation page is static now
* rocks.tarantool.org now in header