[2.3] Examples that points to the DataCollectorListener should be removed.
Removed outdated translations from the official list
Added custom format page to translation component
Link from introduction section
Small fixes
Cleanups
Fixed version for composer install
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
add link to form testing chapter in test section
Added a note about the total deprecation of YUI
Fixed the official name of Node.js
Moved 'contributing' images to their own directory
fix name of the Yaml component

The component name that is used in the code as well as in the issue
tracker used by the symfony/symfony repository is Yaml (instead of
YAML). Therefore, this should also be the name being used in the
documentation.
replace "Symfony2" with "Symfony"
Added a note about the lacking features of Yaml Component
Fixed code highlighting