Internal classes

Hello, could you please take a look?

I have added 3 test cases to show possible issues with internal classes. 
In the first commit I've tried to restrict container to search only for public classes. Sadly, I was not aware of ICompositionRoot implemetation. Moreover, there might already be projects using internal classes with InternalsVisibleToAttribute.

So that's why I've pushed the second one, in which I've added check on public constructor and disabled visibilty check for DynamicMethod.

Let me know your thoughts..