Fixed a bug about --css-dir, --js-dir and --images-dir were not work

- Fix: Directory options was not worked
- Add: "images" directory in CSS
Add Cucumber test

- Add cucumber test
  - with `middleman init MY_PROJECT --template slim`
  - with `--images-dir` option
- Update Slim version
- Change bad method name
- Add travis config file
- Add build status badge and travis ci badge
Merge branch 'release/0.1.0'

Conflicts:
	lib/middleman-slim/template.rb
	lib/middleman-slim/version.rb