The new message syntax:
- Provides 10 commands instead of 60.
- Allows multiple actions to be applied in one call.
The client now returns an non zero exit code when a message fails.
The `is_adjacent` function now handles vacant nodes.
The aforementioned setting, when set, makes the focus movements based on
the distances between the window sides.
The `{prev,next}_leaf` functions were taught not to climb above their
roofs.
