Removed outdated translations from the official list
Added custom format page to translation component
Link from introduction section
Small fixes
Cleanups
Improvements based on comments
Extra improvements based on comments
Fixed wrong indentation
Improved custom formats article based on comments
Added note about exporting SYMFONY_ENV
Added a note about the total deprecation of YUI
Fixed the official name of Node.js
Caution that roles should start with ROLE_

In order to save someone else a few hours of frustration make it clear that the ROLE_ preface is not just for show.
Added a note about the side effects of enabling both PHP and Twig
Add formatting, links, and clarity
Add label book-security-roles
Fix reference label
do not reference services in parameters
Revamped the documentation about "Contributing Docs"
Added missing link