Implement `berks package`

- Fixes #509
Make name attribute optional
Use a custom formatter for package. NullFormater for specs
Read chefignore, unless explicitly told not to
Don't use root_chefignore
Use a common method to define the formatting methods
Fix Null Formatter. Add specs
Merge pull request #510 from sethvargo/berks_package

Implement `berks package`