This is better than `revision = master` because:
- It enables labwc commits to be checked out and build without manually
having to find the right wlroots commit to build with
- The labwc master is always buildable without user intervention even
if there are breaking changes in the wlroots master branch
Suggested in issue #289
This simplifies building as there's no need to manually
git clone subprojects anymore.
Building is now as simple as:
meson build
ninja -C build
In order to update the subprojects, meson provides:
meson subprojects update
