Partially reverting some changes and improving the original content
Making a few changes to the existing description and adding docs for the Formatter Helper
Adding the formatterhelper.rst to index and map
Changing a few wordings as well as code references to methods
Fixing sysmte => system typo
Fixing format issues mentioned by WouterJ
Fix CS for cookbook/form/form_collections
Fixed wrong syntax in book/performance.rst

A double colon was preventing correct displaying
Merge branch '2.0' into 2.1

Conflicts:
	cookbook/testing/doctrine.rst
	cookbook/testing/profiling.rst
Merge branch '2.1'
Added twig.loader definition to dic_tags
Typo, grammar and GitHub UI description changes
Typo: $app->getHelperSet() instead of $this->getHelperSet()
Rephrasing paragraph to make it better understandable
A cookbook article on how to test forms
Remove --dev, replace AbstractType by FormTypeInterface
Fixed code examples in components/di/intro
Fixed code examples in components/di/types
added docs for PrependExtensionInterface
Updating Monolog Config

Updating a misleading `syslog` entry that actually used a stream and added a true `syslogHandler` example so its clearer to people using it.