Describe the bug
Content interface has wireContent method - which marshals bytes to struct implementing Content interface.

Meta property in wireContent, has JSON tag _meta.

type wireContent struct {
        ....
	Meta        Meta              `json:"_meta,omitempty"`
}

however, structs do not have json tag defined, so it expects meta, instead of _meta from byte array.

type ResourceLink struct {
	...
	Meta        Meta
}

We should add json tag for Meta in all structs implementing Content interface. So ResourceLink would become

type ResourceLink struct {
	...
	Meta        Meta              `json:"_meta,omitempty"`
}