v0.5.0: Alpha release

This version adds S6-compatible readiness notification support, and adds support for updating
the "utmp" database when services start/stop (this functionality should be avoided if possible
since the "utmp" database is mostly an historical artifact, and system support is often prone
to issues which allow unprivileged users to prevent updates and deny or delay logins; however,
utilities such as "who" may depend on the database being updated appropriately).

Other changes:

• Add "-u" command line option to force running dinit as a user instance.
• Add a "chain-to" service property to better support recovery services.
• Add a "shares-console" service option to allow running services "on the console" without having
  them own it exclusively.
• Add "inittab-id" and "inittab-line" service settings for utmp support.
• Minor bugfixes.