TODO

Rationalise naming.

Add a way to "deactivate" the cleanup on a tempdir, and move it elsewhere.

Work out a good way to clean up tempdirs because we started after the
peer with the fifo fd closed it. Use systemd's fdstore so the notification
isn't lost because the read-end is closed, or lsof the fifo I guess.

Sort out bus activation.

Sort out the event loop such that we could exit on idle if there are no
tempdirs we need to watch.

Add support for connecting to arbitrary Buses, rather than just the
session bus.

Allow running as a system service and creating the tempdirs with
appropriate permissions such that the peer is allowed to use it

Port code to sd-bus, so there's porting difficulty should there be
interest in moving this functionality into systemd.