Support for fragments

[ecker00]

Seems that the way the client builds it's queries right now it omits fragments, leaving them in the raw query but no reference to their structure. So it sends off requests without fragment details.

Example it generates code like this:

func NewGetAccountMeRequest(url string) (*GetAccountMeRequest, error) {
	b, err := json.Marshal(&GraphQLOperation{
		Query: `query getAccountMe {
  accountMe {
    ...AccountFields
  }
}`,
	})
	if err != nil {
		return nil, err
	}
	req, err := http.NewRequest(http.MethodPost, url, bytes.NewReader(b))
	if err != nil {
		return nil, err
	}
	req.Header.Set("Content-Type", "application/json")
	return &GetAccountMeRequest{req}, nil
}

But it should include a fragment section in the Query like this:

…
Query: `query getAccountMe {
  accountMe {
    ...AccountFields
  }
}
fragment AccountFields on Account {
  id
  email
  username
}`,
…