Simon/differences section robust ecdsa doc

[SimonRastikian]

This PR adds a section to the documentation that declares the differences between our spec and the original scheme.
A couple of additional small typos are repaired in the previous sections.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.56%. Comparing base (8730140) to head (02194c1).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #109      +/-   ##
==========================================
- Coverage   87.60%   87.56%   -0.05%     
==========================================
  Files          43       43              
  Lines        8562     8588      +26     
  Branches     8562     8588      +26     
==========================================
+ Hits         7501     7520      +19     
- Misses        465      469       +4     
- Partials      596      599       +3     

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[gilcu3]

Good explanation!