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