fixed problems with joined inheritance and composite keys

SchemaTool now creates all Id columns not just only the first one.
Insert statement for child entity now contains parameter for additional key columns only once.
inheritance with composite keys

added tests for single table inheritance
Unit tests: cleaned up outdated / unused / commented out code.
Remove dead code
Fix SimpleObjectHydrator behavior when column not exists in fieldMappings, relationMappings and metaMappings
Fixed broken code block in documentation
Missing link to a cookbook in the docs

The cookbook existed in the docs but there was no link to it in the docs.
alias the proxy class on import to avoid "already exists" error
Reverted incorrect typo fix -_-
Typo
Merge pull request #597 from MDrollette/fix-proxy-interface

use the extended proxy interface in the same namespace
Removed unnecessary <?php from the docs
Merge pull request #596 from mnapoli/patch-2

Missing link to a cookbook in the docs
Merge pull request #599 from alexcarol/fix/docs

Removed unnecessary "<?php" from the docs
Added $isIdentifierColumn documentation

I've added the documentation of the argument $isIdentifierColumn since in case of foreign composite keys it doesn't 
Adding EntityManagerDecorator base class as an extension point for EntityManager
Added 'contains' comparison
Added composer.lock to .gitignore
Fixed typos
Merge pull request #607 from pborreli/typos

Fixed typos