docs: public static void main(String[] args) throws IOException{
          MutableRoaringBitmap mrb = MutableRoaringBitmap.bitmapOf(1,2,3,1000); 
          System.out.println("starting with  bitmap "+ mrb);
          ByteBuffer outbb = ByteBuffer.allocate(mrb.serializedSizeInBytes());
          // If there were runs of consecutive values, you could
          // call mrb.runOptimize(); to improve compression 
          mrb.serialize(outbb);
          //
          outbb.flip();
          String serializedstring = Base64.getEncoder().encodeToString(outbb.array());
          ByteBuffer newbb = ByteBuffer.wrap(Base64.getDecoder().decode(serializedstring));
          ImmutableRoaringBitmap irb = new ImmutableRoaringBitmap(newbb);
          System.out.println("read bitmap "+ irb);        
      }