func (s *IssuesService) ListLabelsForMilestone(ctx context.Context, owner string, repo string, number int, opt *ListOptions) ([]*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/milestones/%d/labels", owner, repo, number)
	u, err := addOptions(u, opt)
	if err != nil {
		return nil, nil, err
	}
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	var labels []*Label
	resp, err := s.client.Do(ctx, req, &labels)
	if err != nil {
		return nil, resp, err
	}
	return labels, resp, nil
}
ListLabelsForMilestone lists labels for every issue in a milestone.

GitHub API docs: https://developer.github.com/v3/issues/labels/#get-labels-for-every-issue-in-a-milestone
package github
import (
	"context"
	"fmt"
)
type Label struct {
	URL   *string `json:"url,omitempty"`
	Name  *string `json:"name,omitempty"`
	Color *string `json:"color,omitempty"`
}
func (l Label) String() string {
	return fmt.Sprint(*l.Name)
}
func (s *IssuesService) ListLabels(ctx context.Context, owner string, repo string, opt *ListOptions) ([]*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/labels", owner, repo)
	u, err := addOptions(u, opt)
	if err != nil {
		return nil, nil, err
	}
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	var labels []*Label
	resp, err := s.client.Do(ctx, req, &labels)
	if err != nil {
		return nil, resp, err
	}
	return labels, resp, nil
}
func (s *IssuesService) GetLabel(ctx context.Context, owner string, repo string, name string) (*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/labels/%v", owner, repo, name)
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	label := new(Label)
	resp, err := s.client.Do(ctx, req, label)
	if err != nil {
		return nil, resp, err
	}
	return label, resp, nil
}
func (s *IssuesService) CreateLabel(ctx context.Context, owner string, repo string, label *Label) (*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/labels", owner, repo)
	req, err := s.client.NewRequest("POST", u, label)
	if err != nil {
		return nil, nil, err
	}
	l := new(Label)
	resp, err := s.client.Do(ctx, req, l)
	if err != nil {
		return nil, resp, err
	}
	return l, resp, nil
}
func (s *IssuesService) EditLabel(ctx context.Context, owner string, repo string, name string, label *Label) (*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/labels/%v", owner, repo, name)
	req, err := s.client.NewRequest("PATCH", u, label)
	if err != nil {
		return nil, nil, err
	}
	l := new(Label)
	resp, err := s.client.Do(ctx, req, l)
	if err != nil {
		return nil, resp, err
	}
	return l, resp, nil
}
func (s *IssuesService) DeleteLabel(ctx context.Context, owner string, repo string, name string) (*Response, error) {
	u := fmt.Sprintf("repos/%v/%v/labels/%v", owner, repo, name)
	req, err := s.client.NewRequest("DELETE", u, nil)
	if err != nil {
		return nil, err
	}
	return s.client.Do(ctx, req, nil)
}
func (s *IssuesService) ListLabelsByIssue(ctx context.Context, owner string, repo string, number int, opt *ListOptions) ([]*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels", owner, repo, number)
	u, err := addOptions(u, opt)
	if err != nil {
		return nil, nil, err
	}
	req, err := s.client.NewRequest("GET", u, nil)
	if err != nil {
		return nil, nil, err
	}
	var labels []*Label
	resp, err := s.client.Do(ctx, req, &labels)
	if err != nil {
		return nil, resp, err
	}
	return labels, resp, nil
}
func (s *IssuesService) AddLabelsToIssue(ctx context.Context, owner string, repo string, number int, labels []string) ([]*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels", owner, repo, number)
	req, err := s.client.NewRequest("POST", u, labels)
	if err != nil {
		return nil, nil, err
	}
	var l []*Label
	resp, err := s.client.Do(ctx, req, &l)
	if err != nil {
		return nil, resp, err
	}
	return l, resp, nil
}
func (s *IssuesService) RemoveLabelForIssue(ctx context.Context, owner string, repo string, number int, label string) (*Response, error) {
	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels/%v", owner, repo, number, label)
	req, err := s.client.NewRequest("DELETE", u, nil)
	if err != nil {
		return nil, err
	}
	return s.client.Do(ctx, req, nil)
}
func (s *IssuesService) ReplaceLabelsForIssue(ctx context.Context, owner string, repo string, number int, labels []string) ([]*Label, *Response, error) {
	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels", owner, repo, number)
	req, err := s.client.NewRequest("PUT", u, labels)
	if err != nil {
		return nil, nil, err
	}
	var l []*Label
	resp, err := s.client.Do(ctx, req, &l)
	if err != nil {
		return nil, resp, err
	}
	return l, resp, nil
}
func (s *IssuesService) RemoveLabelsForIssue(ctx context.Context, owner string, repo string, number int) (*Response, error) {
	u := fmt.Sprintf("repos/%v/%v/issues/%d/labels", owner, repo, number)
	req, err := s.client.NewRequest("DELETE", u, nil)
	if err != nil {
		return nil, err
	}
	return s.client.Do(ctx, req, nil)
}