Fixed the KnpMenuBundle and Doctrine requirement

There is no reason to forbid the stable KnpMenu version. Fixes #196
And Doctrine is keeping BC so allowing the next releases is safe (and 2.4 is already in beta)
Update defining_entities.rst

[Doctrine\Common\Annotations\AnnotationException]                                                                                                  
  [Type Error] Attribute "length" of @ORM\Column declared on property Tutorial\BlogBundle\Entity\Post::$title expects a(n) integer, but got string.
Typo TagAdmin / CommentAdmin

There is a little typo TagAdmin => CommentAdmin (in the "Tweak the CommentAdmin class" section)
Merge pull request #198 from stof/patch-1

Fixed the KnpMenuBundle and Doctrine requirement
Migrate code to use the BlockContext
Merge pull request #207 from kasifi/patch-2

Typo TagAdmin / CommentAdmin
Merge pull request #206 from kasifi/patch-1

Update defining_entities.rst : expects a(n) integer, but got string
Merge branch 'sonata/master'

Conflicts:
	composer.json