Subclass IOBase with StreamingBody

[abennett]

Trying to get the ball rolling on #879 again. I'm new to this, so feedback is desired and appreciated. This change passes the tox tests I've run on my laptop.

[codecov-io]

Codecov Report

Merging #1361 into develop will decrease coverage by 0.01%.
The diff coverage is 80%.

@@             Coverage Diff             @@
##           develop    #1361      +/-   ##
===========================================
- Coverage    98.13%   98.12%   -0.02%     
===========================================
  Files           46       46              
  Lines         7736     7740       +4     
===========================================
+ Hits          7592     7595       +3     
- Misses         144      145       +1

Impacted Files	Coverage Δ
botocore/response.py	86.66% <80%> (-1.14%)	⬇️

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