The last desktop and monitor are now deduced from the history.
The stacking order is now independent from the history of the focused
nodes: this prevents hacks on both sides.
All windows are now considered in the stacking algorithm: it prevents
tiled windows from one monitor to appear above the floating windows of
another monitor.
Transfered windows are stacked below the windows of the same kind.
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.
