[Doc] Use Markdown syntax highlighting
Merge branch '2.3' into 2.5

* 2.3:
  [Doc] Use Markdown syntax highlighting
  [Finder] tweaked docs
  [Finder] Add info about possibilities offered by SplFileInfo
  fix components tests
  [Intl] FIxed failing test
  [Intl] Generated the data for ICU version 54-rc
  [EventDispatcher] fix doc bloc on EventDispatcherInterface
  [Validator] Update validators.zh_CN.xlf, fix translation error
  bumped Symfony version to 2.3.21
  updated VERSION for 2.3.20
  update CONTRIBUTORS for 2.3.20
  updated CHANGELOG for 2.3.20
  [Intl] Integrated ICU data into Intl component

Conflicts:
	src/Symfony/Component/HttpKernel/Kernel.php
	src/Symfony/Component/Intl/ResourceBundle/LocaleBundle.php