code: public void map(LongWritable key, Text value, Context context) 
              throws IOException, InterruptedException {
          extractor.processDocument(value, context);
      }
docs: Processes the tokens in the {@code value} and writes a set of tuples
  mapping a word to the other words it co-occurs with and the relative
  position of those co-occurrences.  The key to this method is ignored.
  
  @param key the byte offset of the document in the input corpus
  @param value the document that will be segmented into tokens and
  mapped to cooccurrences
  @param context the context in which this mapper is executing