Annotation and helper classes to add C++ style friend functionality to Java

While Java access modifiers effectively restrict access to classes, methods, and fields, corner cases exist where it is advantageous to expose functionality to a subset of callers outside the preferred scope. For example, one common data model segregates DAOs from handlers and beans in order to restrict public access to the persistence mechanism. However, those beans often need to hold persistence-related data, such as a UID, internally. The DAO must be able to read and modify those values, but their mutators (and often their accessors) should not be accessible publicly. This lightweight library provides a means of achieving that goal.