examples: clean up and update examples

[lukaszstolarczuk]

• add more comments,
• remove stale code,
• make printed messages more verbose.

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This change is 

[codecov-commenter]

Codecov Report

Merging #261 (85bb0bc) into master (3448b96) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #261   +/-   ##
=======================================
  Coverage   88.14%   88.14%           
=======================================
  Files           9        9           
  Lines         776      776           
  Branches      142      142           
=======================================
  Hits          684      684           
  Misses         56       56           
  Partials       36       36           

Flag	Coverage Δ
tests_gcc_debug_cpp17	88.14% <ø> (ø)

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