implement AttributeSource.addImpl()
implement LowerCaseFilter.incrementToken()
implement StandardFilter.incrementToken()
implement StandardTokenizer.incrementToken()
implement AttributeSource.currentState()
implement StandardTokenizerImpl.nextToken()
implement StandardTokenizerImpl.zzRefill()
implement ReusableStringReader using Go's bytes buffer
fix NPE
implement OffsetAttribute ctor
implement TypeAttributeImpl ctor
implement PositionIncrementAttributeImpl.SetPositionIncrement()
implement OffsetAttributeImpl.SetOffset()
implement StopFilter.Accept()
implement DocInverterPerField.processFields()
implement TermsHashPerField.startField()
fix attribute not found issue
implement CharTermAttributeImpl.BytesRef()
implement FreqProxTermsWriterPerField.startField()
implement TermVectorsConsumerPerField.startField()