Add tools for contributing to the project

[kevinfodness]

• Adopt Alley's standard README
• Create CHANGELOG.md for tracking changes per version
• Create CODE_OF_CONDUCT.md to detail the code of conduct that this project uses
• Create CONTRIBUTING.md to provide instructions on how to contribute to the project
• Create CONTRIBUTORS.md to thank GitHub users that have contributed code to the project
• Add plugins as dependencies to composer.json so that a composer install will also install plugins that this plugin depends on and integrates with, facilitating an easier local development setup