Preserve entropy in TokenGenerator

base_convert loses precision on large inputs. Use URL-safe base64_encode instead.
Adding example for services defined in XML
use the new doctrine compiler pass to map the model classes directly
deprecate persistence specific classes
Update Canonicalizer.php

null !== ''

Checking for null is used in particular in the validation
Update Canonicalizer.php

Fixed return value
adjust to factory method
re-adding empty mapping files to keep BC compatibility
add support for mongo
do not have a fatal error if doctrine bridge is too old
adjust to https://github.com/symfony/symfony/pull/7755
add legacy symfony support
added "Annotations" namespace for mongodb
Merge pull request #1099 from bartrail/master

docs: added "Annotation" namespace for MongoDB user and group classes
Enforce POST for /login_check
Used 2.1 syntax
Updated the constraints to allow Symfony 2.3

Closes #1107
Closes #1085
add support for couchdb
updated documentation
added upgrade instructions