ScalaDoc checker

Checks that the ScalaDoc exists for all accessible members:
* ``class``es, ``trait``s, ``case class``es and ``object``s
- methods
- ``val``s, ``var``s and ``type``s

The ScalaDoc's structure must satisfy the parameters of the constructor in case of ``case class``es and ``class``es, or the parameters of methods. In both cases, the ScalaDoc must include the type parameters. Finally, the ScalaDoc must include return description for non-``Unit`` returning methods.

To enable, include

```xml
<check level="error" class="org.scalastyle.scalariform.ScalaDocChecker" enabled="true" />
```