Better interaction with subprocess std[in|out|err]

[gil-obradors]

Needed for interact with big buffer.

Thanks to communicate method implemented with python > 3.
I don't know how to deal with it with python2 ?

https://docs.python.org/3.5/library/subprocess.html#subprocess.Popen.communicate

#251

Official docs:

Warning
Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS   pipe buffers filling up and blocking the child process. 

[codecov]

Codecov Report

Merging #297 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #297      +/-   ##
==========================================
- Coverage   87.09%   87.06%   -0.04%     
==========================================
  Files          16       16              
  Lines        1542     1538       -4     
==========================================
- Hits         1343     1339       -4     
  Misses        199      199              

Impacted Files	Coverage Δ
libtmux/common.py	86.43% <100.00%> (-0.27%)	⬇️

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[gil-obradors]

Official docs says:

Warning
Use communicate() rather than .stdin.write, .stdout.read or .stderr.read to avoid deadlocks due to any of the other OS   pipe buffers filling up and blocking the child process. 

[gil-obradors]

Is ok in python2 and 3!

[tony]

@gil-obradors Merged! This will be in 0.8.5