Revision for the release v0.12

[dr-orlovsky]

This PR adds complete test coverage and documentation required for the release.

It also closes some TODOs and provides final polishing.

[codecov]

Codecov Report

Attention: Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.

Project coverage is 65.7%. Comparing base (0fab906) to head (2357928).
Report is 19 commits behind head on v0.12.

Files with missing lines	Patch %	Lines
commit_verify/src/lib.rs	0.0%	11 Missing ⚠️
single_use_seals/src/lib.rs	42.9%	4 Missing ⚠️
commit_verify/src/embed.rs	0.0%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           v0.12    #195     +/-   ##
=======================================
+ Coverage   57.4%   65.7%   +8.2%     
=======================================
  Files         18      17      -1     
  Lines       1591    1229    -362     
=======================================
- Hits         914     807    -107     
+ Misses       677     422    -255     

Flag	Coverage Δ
rust	65.7% <51.5%> (+8.2%)	⬆️

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