Add install() commands to CMake, lower min C++ standard to 14

[valgur]

Restores the CMake config creation and install() commands from the original repo.

I would like to add this library as a Vcpkg package and a proper CMake installation setup is required for that.

I tested the test_package with C++14 and it built fine with the lower C++ standard.

Bumped the Conan dependency versions to get rid of conflicts. transitive_headers etc are not needed when package_type = "header-library" is set.

I tested the installed output with test_package and it worked fine.

[valgur]

@gegles Are you preferring to keep the CMakeLists.txt simple and not include the standard install() commands? Or are you perhaps planning to handle it yourself?

[gegles]

@valgur, so sorry, I thought this PR was old/stale...

Happy to merge in any improvements you want, please just update and resolve conflicts with the latest.

I/We primarily use conan for package management here and with the official conan recipe here.

So, as long as we keep that going I am good.

The version typically comes from Conan, here, but I/we can figure the best practice for things to work...

Same for the C++ standard... I just bumped it up to C++20 but if we want/need to bring it back down to 14, for better backward compat, I am fine with that as well.