Fixed BC break introduced with 1.3.0

Fixed BC break introduced with #317 and released as 1.3.0

• reported on #317 (comment)
• reported on FriendsOfSymfony/FOSRestBundle#1557
• fixed by #630

Added "hasData" on generic seialization visitors and other minor bugfixes

• Added public hasData function to check if a data key already have been added. #625 (goetas) (based on #466 by mowcixo)
• $context is not used #622 (olvlvl)
• Fix Doctrine PHPCR ODM 2.0 compatibility #605 (wouterj)
• Fixed type-hinting #586 (jgendera)
• Fix multiple handler callbacks in YamlDriver #515 (mpajunen)
• Fixed minor typos #364 (sdaoudi)
• Default $serializeNull to false #317 (steveYeah)
• Missing attribute 'xml-value' in XML Reference #269 (holtkamp)
• Removed unnecessary use statement #262 (dunglas)

HHVM & PHP7 support XML features, bugfixes and infrastructure improvements

This release includes many improvements and bugfixes, some of them are:
#580 HHVM compatibility
#301 Generate namespaced element on XmlList entries
#595 Fix xml-attribute-map for the xml driver
#611 Allow to not skip empty not inline array root node
#610 Allow to use custom serializer with primitive type
#397 Exclude annotation not preventing attempt to find public methods when using AccessType
#608 Composer is not able to resolve a dependency
#550 Generic way to solve setValue on a property which respects its setter
#584 Test on Travis always high and low deps
#583 Update Symfony validator and allow PHPUnit 7
#399 Added travis-ci label
#553 [doc] fix AccessorOrder documentation
#578 Fixed test suite on master
#577 Fix for a broken test: a missing (incorrectly positioned) argument

Some Yaml Fixes & Improved Twig Support

This release improves Twig support and fixes a bug in Yaml serialization.

Further Compatibility Updates and Bug Fixes

This release contains updates for newer PHP versions, and also fixes a few edge-cases. Notable in this release:

• adds convenience toArray and fromArray methods to the Serializer
• better handling of polymorphic objects in collections
• fixes some bugs in the YAML metadata format

Some Features & Fixes

Additions:

• Support for is* and has* methods when changing the accessor policy
• Support for defining the XML namespace on the root node
• Ability to set-up your own driver via the SerializerBuilder
• Better parse error for annotated types

Fixes:

• Several documentation fixes

Misc:

• Composer constraints have been widened to allow to pick more recent versions of dependencies

Several Feature Additions & Bug Fixes

• Native Support for XML Namespaces
• Ability to force type of elements in arrays when serializing
• Usage improvements for YML metadata format (shorter, less verbose for simple things)
• Allow Read-Only to be defined on class level
• Several Improvements to the documentation

Feature Improvements & Enhanced Compatibility

This release contains mostly improvements to existing features and better compatibility for third-party libraries in particular PHPCR.

0.13.0: Merge pull request #130 from youngguns-nl/datatime_doc

fix wrong quote in used in docs