Features:
+* transient units: allow creating auxiliary units with the same call
+
* make BlockIODeviceWeight=, BlockIODeviceBandwidth= runtime settable
* split up BlockIOWeight= and BlockIODeviceWeight=
* split out CreateMachine into systemd-machined
-* "transient" units, i.e units that are not sourced from disk but
- created only transiently via bus calls
-
* introduce new Scope unit type then make logind's session and machine
registration use this to set up cgroups