Fix path to JavaDoc style sheet.
Rewrite JavaDoc of ExcludeCategories.createFilter(Class<?>...).

Remove internal details of the created filter and describe its behaviour instead.
Rewrite JavaDoc of IncludeCategories.createFilter(Class<?>...).

Remove internal details of the created filter and describe its behaviour instead.
Simplify JavaDoc of RunNotifier.fireTestFinished(...).
Remove JavaDoc reference to test class.

The test class is no available by JavaDoc.
Clean up JavaDoc of JUnit38ClassRunner.getAnnotations(...).

Remove empty return and add description of the parameter.
Merge pull request #710 from stefanbirkner/javadoc

Fix JavaDoc errors and warnings.