type Target struct {
Tag string `json:"tag"`
Hashes data.Hashes `json:"hashes"`
}
Target represents the json object of a target of a docker image in notary.
The struct will be used when repository is know so it won'g contain the name of a repository.
GetTargets is a help function called by API to fetch signature information of a given repository.
Per docker's convention the repository should contain the information of endpoint, i.e. it should look
like "192.168.0.1/library/ubuntu", instead of "library/ubuntu" (fqRepo for fully-qualified repo)