by applying this patch, we would be able to extend `freebsd-version`'s features to:
- print verbose information of the base system (using existing `userland_version()` function);
- print verbose information of the running kernel (using existing `running_version()` function);
- print verbose information from a slightly parsed output of `what -qs` (using existing `kernel_version()` function);
- update its manpage, mentioning `__FreeBSD_version` and the references to it.