Provides a means to access the voices that are stored in a jar
file. Every jar file that provides a voice must contain a subclass
of VoiceDirectory. The class must provide a main() function that
calls dumpVoices() or performs an equivalent operation. All
subclasses of VoiceDirectory can be assumed to always be created by
the default constructor (no arguments).
Any jar file that has a subclass of VoiceDirectory must define
certain attributes in its Manifest. "Main-class:" must refer to
the subclass of VoiceDirectory. "Class-Path:" lists the other jar
files upon which this is dependent. For example,
"cmu_us_kal.jar" may be dependent on "en_us.jar" for its lexicon.
The Manifest must also have a "FreeTTSVoiceDefinition: true" entry.