add encoding feature for py3 tarantool.connect

[shveenkov]

if you want to insert binary data in tarantool, msgpack.unpack raise Exception in python3

>>> import tarantool
>>> import msgpack
>>> tnt=tarantool.connect("127.0.0.1", 3301)
>>> tnt.insert("tester", (1, msgpack.packb([1,2,3,"foo"])))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/shveenkov/env_34/lib/python3.4/site-packages/tarantool/connection.py", line 389, in insert
    return self._send_request(request)
  File "/home/shveenkov/env_34/lib/python3.4/site-packages/tarantool/connection.py", line 275, in _send_request
    request)
  File "/home/shveenkov/env_34/lib/python3.4/site-packages/tarantool/connection.py", line 199, in _send_request_wo_reconnect
    response = Response(self, self._read_response())
  File "/home/shveenkov/env_34/lib/python3.4/site-packages/tarantool/response.py", line 57, in __init__
    self._body = unpacker.unpack()
  File "msgpack/_unpacker.pyx", line 427, in msgpack._unpacker.Unpacker.unpack (msgpack/_unpacker.cpp:427)
  File "msgpack/_unpacker.pyx", line 390, in msgpack._unpacker.Unpacker._unpack (msgpack/_unpacker.cpp:390)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0x94 in position 0: invalid start byte
>>> 
>>> 
>>> tnt=tarantool.connect("127.0.0.1", 3301, encoding=None)
>>> tnt.insert("tester", (1, msgpack.packb([1,2,3,"foo"])))