adding KatakanaSpellCheckValidator to SentenceIterator.
separeated testDistance in LevenshteinDistanceTest into each topics.
fixed the indentation.
adding a period and changed the comment setntence.
removed the tailing space.
adding private constructor.
changed the name of the static variable, and introduced public static DEFAULT_ variables and initialized the staic variables by them in static initializer.
Adding period.
removed the tailing space.