Change number int to commentID int64 in PRsService comment methods.

This is a breaking API change that is a part of issue #597. It should've
been applied earlier, but we missed it because the parameter was
misleadingly named number rather than id or commentID.

Rename the parameter to commentID to make it more clear that it's the
comment ID and not the PR ID nor PR number. This should help improve
clarity of the API, and reduce the chance to mix up the IDs.

Also document which PullRequestComment fields need to be set in
EditComment method.

Similar to #886.
Updates #885.
Updates #597.

Author: dmitshur

github/pulls_comments.go

@@ -87,8 +87,8 @@ func (s *PullRequestsService) ListComments(ctx context.Context, owner string, re
 // GetComment fetches the specified pull request comment.
 //
 // GitHub API docs: https://developer.github.com/v3/pulls/comments/#get-a-single-comment
-func (s *PullRequestsService) GetComment(ctx context.Context, owner string, repo string, number int) (*PullRequestComment, *Response, error) {
-	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, number)
+func (s *PullRequestsService) GetComment(ctx context.Context, owner string, repo string, commentID int64) (*PullRequestComment, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, commentID)
 	req, err := s.client.NewRequest("GET", u, nil)
 	if err != nil {
 		return nil, nil, err
@@ -126,10 +126,11 @@ func (s *PullRequestsService) CreateComment(ctx context.Context, owner string, r
 }
 
 // EditComment updates a pull request comment.
+// A non-nil comment.Body must be provided. Other comment fields should be left nil.
 //
 // GitHub API docs: https://developer.github.com/v3/pulls/comments/#edit-a-comment
-func (s *PullRequestsService) EditComment(ctx context.Context, owner string, repo string, number int, comment *PullRequestComment) (*PullRequestComment, *Response, error) {
-	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, number)
+func (s *PullRequestsService) EditComment(ctx context.Context, owner string, repo string, commentID int64, comment *PullRequestComment) (*PullRequestComment, *Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, commentID)
 	req, err := s.client.NewRequest("PATCH", u, comment)
 	if err != nil {
 		return nil, nil, err
@@ -147,8 +148,8 @@ func (s *PullRequestsService) EditComment(ctx context.Context, owner string, rep
 // DeleteComment deletes a pull request comment.
 //
 // GitHub API docs: https://developer.github.com/v3/pulls/comments/#delete-a-comment
-func (s *PullRequestsService) DeleteComment(ctx context.Context, owner string, repo string, number int) (*Response, error) {
-	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, number)
+func (s *PullRequestsService) DeleteComment(ctx context.Context, owner string, repo string, commentID int64) (*Response, error) {
+	u := fmt.Sprintf("repos/%v/%v/pulls/comments/%d", owner, repo, commentID)
 	req, err := s.client.NewRequest("DELETE", u, nil)
 	if err != nil {
 		return nil, err