C++17 deprecated <codecvt>

[mloskot]

We may be interested to address deprecation of <codecvt> and std::wstring_convert and std::wbuffer_convert utilities in C++17 (P0618R0):

• Keep using <codecvt> by default
• Optionally, allow users to enable nanodbc with alternative transcoders (icu, iconv) via CMake option.

This way users concerned about security issues related to use of the <codecvt> will be able to choose an alternative.

[mloskot]

There is no easy way to perform required conversions with the facets. Unless, we implement it on our own which is entirely out of nanodbc scope.

The deprecation does not mean removal. So, until the C++ standard proposes improved conversions or actually removes <codecvt>, we will continue using this <codecvt> features.

[mloskot]

Everyone, I opened #321 with discussion related to C++ standard version.