Add API_LEVEL json mapping. Update README.md

[abonnaudet-ledger]

Description

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(And mention any links to an issue docs)

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)

Breaking changes

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Additional comments

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 35.76%. Comparing base (cb5cfae) to head (b77d5d7).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #789   +/-   ##
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  Coverage   35.76%   35.76%           
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  Files          13       13           
  Lines        1591     1591           
=======================================
  Hits          569      569           
  Misses       1022     1022           

Flag	Coverage Δ
unittests	35.76% <ø> (ø)

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