code: def encode(data):
      
      res = ""
      for i in range(0,len(data), 3):
          if (i+2==len(data)):
              res += _encode3bytes(ord(data[i]), ord(data[i+1]), 0)
          elif (i+1==len(data)):
              res += _encode3bytes(ord(data[i]), 0, 0)
          else:
              res += _encode3bytes(ord(data[i]), ord(data[i+1]), ord(data[i+2]))
      return res
docs: encode the plantuml data which may be compresses in the proper
      encoding for the plantuml server