Completing the Metadata struct inside the CookbookVersion struct

Since I need this info for my program, I just completed the struct with
the missing fields
Merge pull request #36 from svanharmelen/complete_cb_metadata

Completing the Metadata struct inside the CookbookVersion struct
Added some logic to enable uploading cookbooks

With this added code you can now post a cookbook to the community, or
newly released supermarket, API
Merge branch 'supermarket-upload' of https://github.com/svanharmelen/chef-golang into supermarket-upload