Make C++17 the new baseline

[SRombauts]

I am going to release a new version of SQLiteCpp that will be the last one to support C++11
I'll create a maintenance branch "in case of" and I'll update the minimum versions, including CMake, to support C++17 but also C++20 more easily.
This will be the moment to break ABI, to remove or cleanup some old APIs, and make a few important choices

[hellow554]

optinal module support for >=c++20? :)

[SRombauts]

Yes indeed @hellow554, I am even actively testing basic compatibility with C++20 in a separate test app that now run in CI