Produce a Debian package that works on Ubuntu 18.04

[dagood]

To match upstream, the primary artifact from our official builds is a tar.gz file. We should also produce a Deb package, sign it, and host it in a package repository for more convenient installs and automatic upgrading.

The tool I'm most familiar with to do this is FPM (https://github.com/jordansissel/fpm), because .NET [Core] uses it to produce some Linux packages. This would make it easy to make RPM packages, too.

Also consider using a Go module to create the packages. It might be better to consistently use Go libraries rather than use a Ruby gem.