Support for 0install apps
Create a new app with these requirements.
You should call
set_selections immediately after this.
Remove this app and any shell command created with
Get the dates of the available snapshots, starting with the most recent. Used by the "0install whatchanged" command.
Get the current selections. If they're missing or unusable, start a solve to get them. If they're usable but stale, spawn a background update but return immediately.
Place an executable in $PATH that will launch this app.