Add CMake options to disable building tests and examples

[tocic]

When building the library using

cmake -B build/ -S .
cmake --build build/

examples and tests are also built. Is it possible to add CMake options for disabling that (see, e.g., google benchmark)? It's useful for packaging.

[martinus]

I'm bad with cmake, if you are still interested could you do a PR?

[tocic]

Actually, I found out that thanks to #60 you can avoid building tests and examples via building only the nanobench target:

cmake --build "build/" --target "nanobench"

It will not eliminate the configuration step for other targets, but that's not critical. Also, it'd be nice to be able to create dynamic and header-only versions of the library with CMake, but those are separate issues.