[book] some more documentation and cleanups * merged existing facets documentation with the one I've just written and put almost everything within the code * added a note about __depends__ and __recommends__ and about the recommends semantic (extracted from a post on the ml) * added a note about write security checking (extracted from a post on the ml) * fixed some dumb sphinx errors

Relation Query Language (RQL)
=============================

This chapter describes the Relation Query Language syntax and its implementation in CubicWeb.

.. toctree::
   :maxdepth: 2

   intro
   language
   debugging
   implementation