First tagged+signed release

I've been pretty haphazard with versioning -- e.g., I just kind of increment the micro numbers with every commit and increment the minor numbers whenever I feel like it. I've also been pretty haphazard with the rpm releases ... doing it whenever I have the time and feel like enough has changed to warrant it.

Moving forward, I'll be signing all commits and creating release tags regularly (when it makes sense). I'll continue to keep the yum repo at http://people.redhat.com/rsawhill/rpms/ up-to-date, but I'll also be attaching the rpms (signed with my gpg key) to each release here.

Notably, I removed xsos' built-in updating functionality (--update) with the v0.6.0 version (and added warnings for those options in v0.6.1). See #155.