Add DEFAULT_MAX_SEND_SIZE and handle SSLWantWriteError errors

[abhinavsingh]

Fixes #351

[codecov]

Codecov Report

Merging #368 into develop will decrease coverage by 0.08%.
The diff coverage is 50.00%.

@@             Coverage Diff             @@
##           develop     #368      +/-   ##
===========================================
- Coverage    81.52%   81.44%   -0.09%     
===========================================
  Files           72       72              
  Lines         2804     2808       +4     
===========================================
+ Hits          2286     2287       +1     
- Misses         518      521       +3     

Impacted Files	Coverage Δ
proxy/http/proxy/server.py	78.12% <0.00%> (-0.83%)	⬇️
proxy/common/constants.py	100.00% <100.00%> (ø)
proxy/core/connection/connection.py	100.00% <100.00%> (ø)

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