Make naming more consistent with C++17

[lisitsyn]

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[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (develop@d48dc4a). Click here to learn what that means.
The diff coverage is 75%.

@@            Coverage Diff             @@
##             develop    #4080   +/-   ##
==========================================
  Coverage           ?   56.47%           
==========================================
  Files              ?     1333           
  Lines              ?    92770           
  Branches           ?        0           
==========================================
  Hits               ?    52391           
  Misses             ?    40379           
  Partials           ?        0

Impacted Files	Coverage Δ
src/shogun/io/TBOutputFormat.cpp	84.74% <0%> (ø)
src/shogun/lib/any.h	52.29% <100%> (ø)
src/shogun/base/SGObject.h	100% <100%> (ø)
...un/lib/parameter_observers/ParameterObserverCV.cpp	76.92% <100%> (ø)
src/shogun/evaluation/CrossValidation.cpp	95.42% <100%> (ø)

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