Update reference/constraints/Image.rst

Seems that annotations do not support trailing commas in parameter lists like PHP arrays do.
Created intro text of the Twig Reference
Added functions section
Added filter section
Created tags section
Added 'almost core' bundles
add JsonResponse exemple
Remove UniversalClassLoader from debugging recipe (composer autoload covers it)
Update cookbook/form/dynamic_form_generation.rst

fixed event type
Fix typo
Created introduction and toctrees
Created DialogHelper documentation
Update components/http_foundation/sessions.rst

added missing backslash
Update components/http_foundation/sessions.rst

fixed typo
[WIP] FormatterHelper docs
Fixed function name

Function name is not MetadataBag::getLastUpdate() but getLastUsed()
Minor grammar tweak in service container documentation
Allow & Force the 'em' option.

Fix to work with Sf2.1 OptionsResolver
Correcting method names in config component example
Changed function definition to match AbstractTypeExtension interface.