Allow KeyFilters to be applied to listeners

When registering a listener, users should be able to provide a KeyFilter, a simple interface that determines whether a listener is invoked or not based on whether the affected key(s) matches the filter.

The proposed API may overload the addListener(Object listener) method on Cache, adding:

    void addListener(Object listener, KeyFilter filter);

where KeyFilter may be an interface that looks like:

public interface KeyFilter {

   boolean match(Object key);

}