Improve sdk documentation

[nroggeman-ledger]

Description

The goal of this PR is to improve the SDK generated documentation:

• fix warnings
• update NBGL Use Case user manual
• automatically generate documentation in GitHub

Changes include

• Bugfix (non-breaking change that solves an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (change that is not backwards-compatible and/or changes current functionality)
• Tests
• [*] Documentation
• Other (for changes that might not fit in any category)

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 60.19%. Comparing base (dfb10c1) to head (f1656b5).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #711   +/-   ##
=======================================
  Coverage   60.19%   60.19%           
=======================================
  Files          12       12           
  Lines        1726     1726           
=======================================
  Hits         1039     1039           
  Misses        687      687           

Flag	Coverage Δ
unittests	60.19% <ø> (ø)

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[cedelavergne-ledger]

If I am correct, this PR replaces #478