add optional DF-e SOAP client

[rvalyi]

minimalist DF-e SOAP client extracted from larger SOAP experimental branch #133
This code was also adapter from https://github.com/erpbrasil/erpbrasil.edoc/blob/master/src/erpbrasil/edoc/nfe.py under MIT license with proper Copyright attributions Copyright (C) 2019 Luis Felipe Mileo - KMEE
The idea is here we use xsdata bindings with string type checking and brazil-fiscal-client / requests instead of python-zeep and erpbrasil.transmission which is overkill and kind of abandoned.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.02%. Comparing base (92f1816) to head (8d7329e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #140      +/-   ##
==========================================
+ Coverage   93.35%   94.02%   +0.67%     
==========================================
  Files           9       10       +1     
  Lines         301      335      +34     
  Branches       27       29       +2     
==========================================
+ Hits          281      315      +34     
  Misses         10       10              
  Partials       10       10              

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