User message signing and verification

[janezpodhostnik]

closes: #36

Add user message signing and verification

[codecov-commenter]

Codecov Report

Merging #37 (f30c92a) into master (1b8211e) will increase coverage by 0.47%.
The diff coverage is 91.30%.

@@            Coverage Diff             @@
##           master      #37      +/-   ##
==========================================
+ Coverage   80.70%   81.17%   +0.47%     
==========================================
  Files          26       28       +2     
  Lines        1513     1562      +49     
  Branches       92       93       +1     
==========================================
+ Hits         1221     1268      +47     
- Misses        276      277       +1     
- Partials       16       17       +1     

Flag	Coverage Δ
unittests	81.17% <91.30%> (+0.47%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
flow_py_sdk/tx.py	53.95% <33.33%> (-0.84%)	⬇️
flow_py_sdk/signer/signer.py	90.00% <84.61%> (-10.00%)	⬇️
flow_py_sdk/signer/in_memory_verifier.py	90.90% <90.90%> (ø)
flow_py_sdk/__init__.py	100.00% <100.00%> (ø)
flow_py_sdk/signer/__init__.py	100.00% <100.00%> (ø)
flow_py_sdk/signer/in_memory_signer.py	100.00% <100.00%> (ø)
flow_py_sdk/signer/verifier.py	100.00% <100.00%> (ø)
flow_py_sdk/templates.py	55.55% <100.00%> (+2.61%)	⬆️

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[oeway]

Thanks a lot @janezpodhostnik I will give it a try!