Update validations to behave like real validations on config
Add an exception for a missing config value
Add artifactory_* configuration sections
Remove S3 Publisher validations from publisher

This commit moves the validations into the config object. Attempting to
access a value such as release_s3_access_key will throw an exception.
Remove Rubocop and Guard

Rubocop, I am so over you. Like, you have no idea. You used to be a
really good friend, but our OCDs have now misaligned. I fear I will be
writing my own in the future.
Fix RSpec deprecation warnings
Refactor publishers into their own CLI subclass
Add SHA128 info to packages and metadata
Fix a bug in thor when asking for help on subsubcommands
Add more information to the generated package metadata
Add artifactory as a development dependency
Add artifactory publisher
Remove extra newline that slipped in
Fix old comment in Publisher CLI
Fix copy-paste from S3 publisher
Remove old reference to InvalidS3Configuration error