Better tests. As part of that, I had to break TibetanMachineWeb into
TibetanMachineWeb+THDLWylieConstants, because I don't want the
class-wide initialization code from TibetanMachineWeb causing errors
in LegalTshegBarTest.
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.
