Block class declarations

The JLS allows class declarations in blocks, which is not supported (as far as I can see) in (J)CodeModel.
See http://docs.oracle.com/javase/specs/jls/se7/html/jls-14.html#jls-14.2 for reference.

Now, I haven't actually seen anyone using this feature ever, so it might not be worth wasting time on it.
Maybe if I get bored I'll write support for it in a few weeks.
