Merge pull request #12 from whargrove/master

Refresh stage
Updated Gemfile.lock after bundling updated gems, Added .ruby-version to .gitignore for development.
Added authorize_registration method to check for the user's IP address and compare against value in CONFIG to determine if the user is authorized to create a new user.
Removed comments to re-enable user registration. Added before_action to enforce authorize_registration on user controller actions.
Updated README.md and added ip_address key to application.example.yml.
Updated gem versions.
Merge branch 'user_registration' into stage
Merge branch 'stage'