Add meson build system

[zeenix]

This is what will likely be expected of a modern system service, especially from package managers and/or folks who are used to building existing bus implementations themselves for any reason.

This will complicate the build itself. We'll need to figure out if we want to go the usual hacks to call Cargo from meson or use the latest cargo support in meson.

OTOH it will make it very easy to (un)install the binary and auxiliary data files.