Create github singleton class.
Implement Deserializable mixin to conveniently update attributes from Mash returend by Octokit.
Fix a serious bug in Deserializable.
Implement login and pull_requests features of Github singleton.
Inherit attributes list from superclass.
Make sure models all have correct mixins and attributes.
Rename duplicate class names in tests to avoid conflict.
Move UnprocessableState into Errors module.
Use require_relative for local modules.