Miscellaneous enhancements and a fix

In my ongoing effort to run [SCIFIO](http://scif.io/) -- a powerful Java library for loading and saving images in all kinds of formats -- via Avian, I noticed some missing pieces, and a NullPointerException that was thrown in ```Field#getAnnotation```.

The only thing I am not quite sure about is the specifics of the implementation of _Implement Class#getDeclaredClasses_: did I do it correctly? Or is it preferred not to touch/not to leave things in ```ClassAddendum```?