Update C++ to C++17.

[galanCA]

This pull request updates the btwxt to C++ 17.

On visual studio I make sure it compile in C++ 17.
It also build and passed all the local test, as well as the CI.

[codecov-commenter]

Codecov Report

Merging #16 (5c8bde9) into develop (d014b89) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop      #16   +/-   ##
========================================
  Coverage    84.30%   84.30%           
========================================
  Files            7        7           
  Lines          433      433           
========================================
  Hits           365      365           
  Misses          68       68           

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