* Reworked phantom reference handling.
- Replaced IDecRefQueue with a new Z3ReferenceQueue class
- Z3ReferenceQueue manages custom subclasses of phantom references in a doubly-linked list
- Replaced all subclasses of IDecRefQueue with subclasses of Z3ReferenceQueue.Reference. These custom reference classes are embedded in the class they reference count.
- Context now owns a single Z3ReferenceQueue for all types of references.
* Made Statistics.Entry a static subclass
* Made Context.close idempotent (as recommended)
* Update CMakeLists.txt for building the Java API.
* Updated CMakeLists.txt again.
* Use correct SuppressWarning annotation to silence the compiler
* Formatting
