UnicodeCodepointToThdlWylie.java.
Added a new class, UnicodeGraphemeCluster, that can tell you
the components of a grapheme cluster from top to bottom. It does not
yet have good error checking; it is not yet finished.
Next is to parse clean Unicode into GraphemeClusters. After that comes
scanning dirty Unicode into best-guess GraphemeClusters, and scanning
dirty Unicode to get nice error messages.
