WP-CLI integration + testing

[HongPong]

Getting some kind of integration with WP-CLI would be very helpful for most people, even if it is just status readouts to start with. Also tests should be included. Certainly if this plugin is widely used, this would help a lot.

• https://make.wordpress.org/cli/handbook/internal-api/wp-cli-add-command/
• https://make.wordpress.org/cli/handbook/plugin-unit-tests/
• https://developer.wordpress.org/cli/commands/scaffold/plugin-tests/
• Equiv for themes: https://developer.wordpress.org/cli/commands/scaffold/theme-tests/
• https://deliciousbrains.com/deploying-wordpress-plugins-travis/
• https://johnblackbourn.com/reducing-travis-ci-build-times-for-wordpress-projects/
• https://www.tychesoftwares.com/a-look-at-how-woocommerce-tests-using-continuous-integration/
• https://wordpress.org/plugins/gitium/ and https://www.presslabs.com/code/gitium/
• https://shubhampandey.in/integrating-travis-ci-wordpress-theme/
• https://seravo.fi/2015/continuous-integration-testing-for-wordpress-plugins-on-github-using-travis-ci
• https://joemcgill.net/2017/02/setting-wordpress-tests-circleci-wp-cli/