Fix a bug about css
Add cucumber test

- Add simple cucumber test
  with `middleman init MY_PROJECT --template slim`
- Update Slim version
Merge branch 'feature/cucumber_test' into develop
Add cucumber test about --images-dir option

- change bad method name
Add travis config file
Update version number to v0.1.0
Add build status badge and travis ci badge
Change method name

Middleman's default template use `build_scaffold!` method.
ReOrganize gemspec and Gemfile

- middleman-slim.gemspec has all gem dependencies.
- Gemfile is Simplified.
- Gemfile.tt is added some gems.
- Remove some lines from env.rb because these lines are not used.
Merge branch 'develop'

Conflicts:
	Gemfile
	features/support/env.rb
	lib/middleman-slim/template/shared/Gemfile.tt
	lib/middleman-slim/version.rb
	middleman-slim.gemspec