Analyzer: add skeleton
Merge branch 'master' into tokenizer
Analyzer: simple analyzer
Pass analyzer class, not tokenizer
add abstract Indexer
remove IndexReader and IndexWriter use indexer instead
rewrite Terms class
delete PostingList and PostingListEntry
remove IndexTerm class
remove useless field
merge Duplicates functionality to Documents
remove DefaultIndex and implement it in DefaultIndexer
check for null value
Indexer: implement update document
rename can replace indexed file from unindexed file
commit database on each document visit

prevent commit method to throw an exception.
Should be really slow, need to split document visit to more thread.
close database manually
Searcher: add skeleton
move search routine to Search class
WatcherThread: do not add document if it is already exist