QDox model ctors need to be public

Over the last several weeks, the access to the constructors was changed from "public" to "protected". This breaks clients that need to create model objects, including objects created as mock for testing. (The timing of this change is almost more disturbing than the change itself though...)

Some manner of creating objects that conform to the model interfaces must be provided to QDox clients, whether in the form of public constructors, factory interfaces for model objects or JavaDocBuilder, or extracted interfaces.

The final option provides the most flexibility for the QDox maintainers. Extracting interfaces does not at all limit their ability to be changed, but does encourage developers away from the bindings that clients must otherwise make on the internal interfaces of the library. If the interfaces change between versions, so be it. As is true with any jar, a maintainer of a client to that jar must link against that new jar in order to take advantage of the new functionality.