Add string() methods to get the printable information

[saikishor]

No description provided.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.13%. Comparing base (18c4b12) to head (cae03d8).
⚠️ Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #547      +/-   ##
==========================================
- Coverage   83.13%   83.13%   -0.01%     
==========================================
  Files          29       29              
  Lines        1981     1963      -18     
  Branches      110      110              
==========================================
- Hits         1647     1632      -15     
+ Misses        268      265       -3     
  Partials       66       66              

Flag	Coverage Δ
unittests	83.13% <ø> (-0.01%)	⬇️

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Files with missing lines	Coverage Δ
control_toolbox/include/control_toolbox/pid.hpp	64.78% <ø> (ø)

... and 2 files with indirect coverage changes

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