code: static String encodeEntry(Entry<String, Point2d[]> entry) {
          StringBuilder sb = new StringBuilder();
          sb.append(entry.getKey());
          sb.append(' ');
          sb.append(encodeCoordinates(entry.getValue()));
          return sb.toString();
      }
docs: Encodes an entry in a compact string representation. The encoded entry is a SMILES string
  with the coordinates suffixed in binary.
  
  @param entry the entry to encode
  @return encoded entry