Add unit test for the 3rd package-info.java example.

[jmax01]

Currently there is not a unit test that matches the 3rd example in the package-info.java file:

 assert_().about(javaSource())
     .that(JavaFileObjects.forResource("HelloWorld.java"))
     .processedWith(new MyAnnotationProcessor())
        .compilesWithoutError()
        .and().generatesSources(JavaFileObjects.forResource("GeneratedHelloWorld.java"));

As I (and others) have had difficulty getting this to work a unit test for this example would be helpful.