Import LuceneLoggerBackend in LuceneLogger
Add javadoc description to LuceneLoggerBackend
Fix indentation in LuceneLoggerBackend
Initialize IndexWriter separately in LuceneLoggerBackend

It is initialized apart from Analyzer, Directory, and etc
Close lucene classes when receiving a CLOSE signal
Modify error description in LuceneLoggerBackend
Destroy 0MQ context in LuceneLogger.close