Support multiple roles applications

Allow passing more than one role to be applied.

```
$ sunzi create
      create  sunzi/.gitignore
      create  sunzi/sunzi.yml
      create  sunzi/install.sh
      create  sunzi/recipes/sunzi.sh
      create  sunzi/roles/db.sh
      create  sunzi/roles/web.sh
      create  sunzi/files/.gitkeep
$ cd sunzi
$ sunzi compile db web
      create  compiled/attributes/environment
      create  compiled/attributes/ruby_version
      create  compiled/recipes/rvm.sh
      create  compiled/recipes/sunzi.sh
      create  compiled/roles/db.sh
      create  compiled/roles/web.sh
      create  compiled/_install.sh
      create  compiled/install.sh
```