Allow class declaration with fully-qualified name

It would be nice to have the ability to declare classes without explicit nesting.

Currently:

``` ruby
class Foo {
  class Bar {
    class UhOh { }
  }
}
```

This can quickly become a bit cumbersome.

Suggestion:

``` ruby
class Foo::Bar::UhOh {
  def init { 'yay } 
}
```
