Corrected a typo in field mapping
Merge pull request #13 from benjaminpaap/fix/doctrine-mapping

Corrected a typo in field mapping
Now using `ReflectionClass::implementsInterface`

Thanks to @GromNaN. This feels so much more correct. There is no need to
instantiate every entity anymore.
Merge pull request #14 from benjaminpaap/feature/subscriber-check-abstract

TablePrefixSubscriber also tries to instantiate abstract classes
Added a `WordpressContentInterface`

Comment and Post entities share a common `getContent` method. Made an
interface for that to better react on these types.
Added the fluent interface for all entities

See: http://en.wikipedia.org/wiki/Fluent_interface
Fixed Entity Mappings
Fixed Service Definition