Issue #5: expand test suite to cover Unicode16 and Unicode32 strings. Move String>>neoJsonOn: to CharacterCollection>>neoJsonOn:
 so that multi-byte strings are covered. Unicode32 string test cases are failing:

74 run, 71 passes, 0 expected defects, 3 failures, 0 errors, 0 unexpected passes
  75 tests
  74 run ['done']
  71 passes
  0 expected defects
  3 failures
  0 errors
  0 unexpected passes