message: improve micropython contract example
diff: import eoslib
  +try:
  + import struct
  +except Exception as e:
  + import ustruct as struct
  +mp=eoslib.N('micropython')
  print('hello,world from mp')
  def init():
  print('hello from micropython.init')
  + print('--------------------------------')
  + db_keys = struct.pack('Q', eoslib.N('currency'))
  + values = struct.pack('QQ', 0x778899, 0x112233)
  + print("mp:", mp)
  + print(eoslib.uint64_to_string(mp))
  + ret = eoslib.store(mp, mp, db_keys, 0, values)
  + print('++++++++eoslib.store return:',ret)
  def apply(name, type):
  print(name, type)
  