Features:
* add a new specifier to unit files that figures out the DDI the unit file is
- from, tracing trough overlayfs, DM, loopback block device.
+ from, tracing through overlayfs, DM, loopback block device.
* in os-release define a field that can be initialized at build time from
SOURCE_DATE_EPOCH (maybe even under that name?). Would then be used to