Persistent session support

[pavlushkin]

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0467a84) 97.48% compared to head (24812a6) 97.50%.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #118      +/-   ##
==========================================
+ Coverage   97.48%   97.50%   +0.01%     
==========================================
  Files           8        8              
  Lines         717      722       +5     
==========================================
+ Hits          699      704       +5     
  Misses         18       18              

Flag	Coverage Δ
unittests	97.50% <100.00%> (+0.01%)	:arrow_up:

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[ruscoder]

Good feature. I suggest actualize it and get it merged. The only thing that looks confusing to me is naming - http_session, I suggest renaming it to just session or aiohttp_session or client_session.