Update coding standards

Removing underscores from property/method names and change use statements to PSR-2
Removed unneeded escape character

Removed backslash
Merge pull request #649 from calumbrodie/patch-1

Update coding standards in change tracking cookbook entry
Fixed typo in SQLFilter (use statement ClassMetadata)
Merge pull request #651 from EuKov/patch-1

Fixed typo in SQLFilter (use statement ClassMetadata)
Fixed entities path

In the tutorial, the user is told to create a new file in the '/src' folder, and the 'entities' folder is never referenced. Updating the SQLite schema according to the tutorial fails with the 'No Metadata Classes to process.' message. Changing the folder to '/src' fixes this, ostensibly.
Merge pull request #652 from dannykopping/patch-1

Fixed entities path
Fix DDC-2415
Merge pull request #653 from FabioBatSilva/DDC-2415

[DDC-2415] Fix CustomIdGenerator inheritance
Fix DDC-2409
[DBAL-483] Pass default values to DBAL mapping layer correctly to fix default comparision bug.
Merge branch 'DBAL-483'
Merge pull request #655 from FabioBatSilva/DDC-2409

[DDC-2409] Fix merge association STATE_NEW
Simplify condition of previous commit (5cdc73e)
[DDC-2106] Fix entity as parameter value when its managed but not yet with identifier.
Merge branch 'DDC-2106'
[DDC-1984] Throw exception if passing null into UnitOfWork#lock() - which can happen when EntityManager#find() tries to lock entity that was just deleted by another process.
Merge branch 'DDC-1984'
[DDC-1998] Pass types to Connection#delete() to allow custom conversions to happen.
Merge branch 'DDC-1998'