Unify CMake practices across all Beman libraries

[ednolan]

Currently, not all libraries use CMake the same way as exemplar does. We should unify our CMake practices across all Beman libraries.

[ednolan]

This is blocked on #175.

[ClausKlein]

We do have a beman-tidy script, or not?

This should be run on CI and/or as pre-commit hook

Do we have a written CMake usage / best practices guide?