Adds chef generate repo support

Creates a chef-repo that is identical to the current state of
github's opscode/chef-repo repository.

Has options that match those of knife cookbook create, for
license, copyright holder, etc.

Includes --policy-only support, which puts the cookbook
directory into .gitignore and adds a different README
file.
Any update needed here (or the next paragraph)? Dunno if this is a good place to mention that there's a different workflow you could be using...