rename Tokenizer to StandardTokenizer
create abstract Tokenizer class

old Tokenizer class is now StandardTokenizer
add WhitespaceTokenizer
custom tokenizer
StandardTokenizer: use WhiteSpaceTokenizer
add NGramFilter
ngram is a new token type
update token type to only WORD and NGRAM
diffrentiate between word and n-gram
remove dependency to lucene
fix buffer exhaust problem
encapsulate reading byte
separate TokenType enum from Tokenizer class file
unified Tokenizer.Token and Token class
search token should match index token
remove some unnecessary code
add LowerCaseFilter and TokenFilter abstract class
App: fix typo
DocumentFile: index file name too
Index N-Gram too