Add cookbook dependencies
Validate Chef version constraints with ActiveModel
API specs share tarballs created on-demand

This ensures that our API spec metadata.json specifies both platform
dependencies and cookbook dependencies. This way, we're covering more of the
codebase, especially in Cookbook#publish_version!
Connect cookbook dependencies with the cookbooks they depend on, if possible
Merge pull request #259 from opscode/cookbook-dependencies

Cookbook dependencies