Improve CMake build scripts about munt

[dreamer]

@sergm I suggest you spend some time investigating Meson - perhaps switching the buildsystem will be beneficial for the project.

[sergm]

I did look at Meson some time ago. Being based on a multi-purpose language, it seems powerful, somewhat similar to gradle and waf in spirit, I think. But atm, there is no plan to switch, as CMake seems well supported, widely available and "it does its work" so far... It'd be a good choice a while ago, when we got away from autotools, though.

[AndersonTorres]

Correct me if I'm wrong, but according to this, all multiple projects/packages inside this monorepo will receive the same numbered version tag?

[sergm]

Well... To be fair, there is no strict relation between version numbers among the projects, except the fact that the "munt" tag currently matches the library version. Maybe a better idea would be to use the year.release scheme here, I'm not too sure yet.

And yes, all tags are indeed visible in a single git repo, but each tag is prefixed with the project ID, so we may distinguish what project exactly is tagged.