Pickle serializer/deserializer implementation.

[DoeringChristian]

I have copied the yaml serializer and deserializer implementation and adapted it to work with pickle.
I'm not quite sure if this will find uses but I think it is nice to have direct serialization/deserialisation to pickle.
Added from_pickle and to_pickle methods to the tests.

[codecov]

Codecov Report

Base: 90.74% // Head: 90.84% // Increases project coverage by +0.10% 🎉

Coverage data is based on head (1a0f7e9) compared to base (3f3de51).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
+ Coverage   90.74%   90.84%   +0.10%     
==========================================
  Files          10       11       +1     
  Lines        1599     1617      +18     
  Branches      342      342              
==========================================
+ Hits         1451     1469      +18     
  Misses        105      105              
  Partials       43       43              

Impacted Files	Coverage Δ
serde/pickle.py	100.00% <100.00%> (ø)

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[yukinarit]

LGTM, Thank you!