Several improvements to the unicode library:

Several improvements to the unicode library:

  o  All tables are now const.
  o  Redefined the categories:
	- now using _U_* instead of _C_*
	- introduced _U_LETTER modified with either _U_UPPER or _U_LOWER
	  or none (titlecase letters, letter modifiers etc.)
  o  Added the ligature expansions and _U_LIGATURE.
  o  Minor cleanups.