Update to rework 1.0.0

This PR addresses #8 and refactors parts of the task that didn't follow the patterns used in grunt-contrib plugins.

* Remove `vendors` option (not supported in rework 1.0)
* Remove evil support for built-in rework plugins, closes #10
* Log errors when invalid plugin is provided
* Refactor test directory structure to make more sense
* Remove grunt plugins from package.json
* Add tests for plugin usage
* Update README
* Add grunt to peerDependencies
* Remove dependency on grunt-cli in favor of travis before_script
* Remove bin folder, not required for grunt plugins
* Bump version to 0.1.0