Binary support

[JonnoFTW]

Added binary support per #156

I've added some more tests to cover more cases surrounding binary encodings. If you pass a string to a binary field, it will come out as a bytes type on the other end.

The work here builds off #163 , so that will probably need to be merged before this one.

[codecov]

Codecov Report

Merging #164 (80264d7) into master (02924c7) will increase coverage by 0.94%.
The diff coverage is 89.12%.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
+ Coverage   83.37%   84.31%   +0.94%     
==========================================
  Files          43       44       +1     
  Lines        3939     4164     +225     
==========================================
+ Hits         3284     3511     +227     
+ Misses        655      653       -2     

Impacted Files	Coverage Δ
thriftpy2/contrib/aio/rpc.py	84.44% <ø> (ø)
thriftpy2/contrib/aio/protocol/binary.py	55.73% <21.42%> (-2.07%)	⬇️
thriftpy2/contrib/aio/protocol/compact.py	60.17% <50.00%> (-0.82%)	⬇️
thriftpy2/protocol/binary.py	89.25% <76.47%> (-1.06%)	⬇️
thriftpy2/protocol/compact.py	84.54% <91.30%> (+2.27%)	⬆️
thriftpy2/protocol/apache_json.py	97.59% <97.59%> (ø)
thriftpy2/protocol/__init__.py	87.50% <100.00%> (+0.83%)	⬆️
thriftpy2/protocol/json.py	96.74% <100.00%> (+13.98%)	⬆️
thriftpy2/thrift.py	90.39% <100.00%> (ø)
... and 3 more

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[JonnoFTW]

@ethe are you able to look at this at some point?

[ethe]

I will take a look at it, could you please remove [WIP] in the title?

[JonnoFTW]

@ethe I have fixed the title.

[ethe]

I have a question, does it break the compatibility? If the user defines a binary type and treats it as a string before, what happened after this commit merged?

[ethe]

Maybe we should consider that only turn on this feature in JSON protocol and do not modify others, or turn off it as default in other protocols.

[JonnoFTW]

@ethe please check tests/test_all_protocols_binary_field.py for a test case on how binary fields are treated. I think the best behaviour would be that the type specified in the thrift file is what you get when deserializing.

If a string is passed to a binary field, when deserialised you always get a binary. Conversely, if a binary is passed to a string field, it should be stringified (if possible) when deserializing.