import artifact code from release.rb
upgrade fpm to use internal api correctly

the yak that would not shave
render metadata after package creation
add checksums to flat metadata
make both rhel and centos report "el"
Create implementation class for simple S3 release
add callbacks for after upload so we can add UI
Always attempt to load config, message if there isn't one
implement `release package` command (rm placeholder)

Adds `release` namespace with `package` subcommand. The intent is to
also add a omnitruck-compatible release command (currently in the
jenkins/ directory of omnibus-chef and -server repos) in this namespace.

Implemented package command releases a single package with associated
metadata file to a single S3 bucket.
Remove deleted TODO.md from yardopts
Use shellout! via omnibus util instead of directly