v0.20.0 finishes a set of breaking changes:
 - Various resources (config, environment, and runtime files) are consolidated
   into `uwsm` subdirs. Old paths no longer considered.
 - Automatic finalization mechanism: existing plugins will no longer prevent
   compositors from signaling unit readiness and putting vars in activation
   environments.

Props to @YaLTeR for pointing me into the right direction with autofinaization.