First pass at framework with testing, rake, etc

- Due to Foodcritic and how Supermarket renders README.md, rename README.markdown to README.md
- Add some default files for .gitignore, .rubocop.yml, .kitchen.yml, etc
- Added a default recipe to install curl and create a dummy chef resource, just as an example to start with
- Add chefspec and test-kitchen/serverspec default test suites that just test the current default recipe
- Add test fixtures like a wrapper cookbook to test how downstream cookbooks might use this one
- Add lengthy documentation on testing, how it works in this cookbook, etc