skipIfNull parameter in @Relation
Renamed skip_if_null to exlude_if

- Now checks for the value and skips
- Added unit tests
Fix pagerfanta handlers when the result isn't an array but a traversable object
Updated README
Merge pull request #42 from baldurrensch/skip_if_null

Ability to exclude links based on criteria
Merge branch 'master' into metadata-stack-goodness

Conflicts:
	Tests/Functional/ControllerTest.php