Add option to decode responses in python3

[owenstranathan]

In redis-py on python 3 we have the option to construct our redis class with the kwarg
decode_responses=True which will decode bytes received from redis requests to python 3 strings ('utf-8')

This is really useful behavior because without it we have to decode all bytes before we use them, (not hard but tedious).

This PR adds a setting to enable that behavior in python versions > (3,)

[codecov]

Codecov Report

Merging #146 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #146      +/-   ##
==========================================
+ Coverage   92.85%   92.88%   +0.02%     
==========================================
  Files          18       18              
  Lines         728      731       +3     
  Branches       57       58       +1     
==========================================
+ Hits          676      679       +3     
  Misses         36       36              
  Partials       16       16

Impacted Files	Coverage Δ
src/scrapy_redis/connection.py	100% <100%> (ø)	⬆️

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[owenstranathan]

are there any maintainers for this project?

[sumous]

are there any maintainers for this project?

May be not！Should we maintain it？