Fix missing string_view path method

[karjonas]

This is needed to be able to compile using a c++17 standard library for both gcc and clang.

[gulrak]

Indeed, that helps. I think I'll add C++17 tests to the CI scripts in the next days, to ensure stable support against C++17.

Thanks for supplying the fix!

[karjonas]

Thanks, nice library!

[gulrak]

Hi @karjonas! There is interest to move to the more liberal MIT license. To allow this to happen, I would like to ask you as a contributor, to agree to this re-licensing with a reply to issue #47