Features:
+* Add timeout to early-boot, and shut down the system if it is hit. Solves the laptop-in-bag problem and is useful for embedded cases
+
* sd-resolve: add callback api
* ImmutableSystem=yes/no or so to mount /usr, /boot read-only/invisible, and leave /var and /etc writable
ReadOnlyDirectories=... for whitelisting files for a service.
* sd-bus:
+ - make AddMatch calls on dbus1 transports async
- when kdbus doesn't take our message without memfds, try again with memfds
- systemd-bus-proxyd needs to enforce good old XML policy
- port exit-on-idle logic to byebye ioctl