Update reference/constraints/Image.rst

Seems that annotations do not support trailing commas in parameter lists like PHP arrays do.
Added failure_path param
Created intro text of the Twig Reference
Added functions section
Added filter section
Created tags section
Added 'almost core' bundles
Added missing dot in property path assembly.
Adding link to how to render templates
Adding link to @ParamConverter
Changed uses of we in security cookbooks
Removed space around dot operator.
[Book/installation] Fixed "image file not readable" warning
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