Update BranchesService Methods to Conform to v4 API (#157)

* CI: always test on the latest bugfix Go releases (#154)

* Remove unnecessary fmt.Sprintf call (#153)

* Fix typo in user 404 error (#155)

* Update BranchesService Methods.

This change breaks backwards compatibility.

The BranchesService methods were almost all inconsistent with other Services and not supplying all available options. Also updated all documentation links.

The Branch struct now includes all properties exported by the v3 API.
ListBranches takes a new ListBranchesOptions struct for pagination.
Added the ability to configure the branch protection in line with API documentation.
Added a new DeleteMergedBranches which is part of the branches page.

* Restore API doc links

branches.go

@@ -24,16 +24,14 @@ import (
 // BranchesService handles communication with the branch related methods
 // of the GitLab API.
 //
-// GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md
+// GitLab API docs: https://docs.gitlab.com/ce/api/branches.html
 type BranchesService struct {
 	client *Client
 }
 
 // Branch represents a GitLab branch.
 //
-// GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md
+// GitLab API docs: https://docs.gitlab.com/ce/api/branches.html
 type Branch struct {
 	Commit             *Commit `json:"commit"`
 	Name               string  `json:"name"`
@@ -50,7 +48,7 @@ func (b Branch) String() string {
 // ListBranchesOptions represents the available ListBranches() options.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#list-repository-branches
+// https://docs.gitlab.com/ce/api/branches.html#list-repository-branches
 type ListBranchesOptions struct {
 	ListOptions
 }
@@ -59,7 +57,7 @@ type ListBranchesOptions struct {
 // name alphabetically.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#list-repository-branches
+// https://docs.gitlab.com/ce/api/branches.html#list-repository-branches
 func (s *BranchesService) ListBranches(pid interface{}, opts *ListBranchesOptions, options ...OptionFunc) ([]*Branch, *Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -84,7 +82,7 @@ func (s *BranchesService) ListBranches(pid interface{}, opts *ListBranchesOption
 // GetBranch gets a single project repository branch.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#get-single-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#get-single-repository-branch
 func (s *BranchesService) GetBranch(pid interface{}, branch string, options ...OptionFunc) (*Branch, *Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -109,7 +107,7 @@ func (s *BranchesService) GetBranch(pid interface{}, branch string, options ...O
 // ProtectBranchOptions represents the available ProtectBranch() options.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#protect-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#protect-repository-branch
 type ProtectBranchOptions struct {
 	DevelopersCanPush  *bool `url:"developers_can_push,omitempty" json:"developers_can_push,omitempty"`
 	DevelopersCanMerge *bool `url:"developers_can_merge,omitempty" json:"developers_can_merge,omitempty"`
@@ -120,7 +118,7 @@ type ProtectBranchOptions struct {
 // still returns a 200 OK status code.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#protect-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#protect-repository-branch
 func (s *BranchesService) ProtectBranch(pid interface{}, branch string, opts *ProtectBranchOptions, options ...OptionFunc) (*Branch, *Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -147,7 +145,7 @@ func (s *BranchesService) ProtectBranch(pid interface{}, branch string, opts *Pr
 // still returns a 200 OK status code.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#unprotect-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#unprotect-repository-branch
 func (s *BranchesService) UnprotectBranch(pid interface{}, branch string, options ...OptionFunc) (*Branch, *Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -172,7 +170,7 @@ func (s *BranchesService) UnprotectBranch(pid interface{}, branch string, option
 // CreateBranchOptions represents the available CreateBranch() options.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#create-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#create-repository-branch
 type CreateBranchOptions struct {
 	BranchName *string `url:"branch_name,omitempty" json:"branch_name,omitempty"`
 	Ref        *string `url:"ref,omitempty" json:"ref,omitempty"`
@@ -181,7 +179,7 @@ type CreateBranchOptions struct {
 // CreateBranch creates branch from commit SHA or existing branch.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#create-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#create-repository-branch
 func (s *BranchesService) CreateBranch(pid interface{}, opt *CreateBranchOptions, options ...OptionFunc) (*Branch, *Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -206,7 +204,7 @@ func (s *BranchesService) CreateBranch(pid interface{}, opt *CreateBranchOptions
 // DeleteBranch deletes an existing branch.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#delete-repository-branch
+// https://docs.gitlab.com/ce/api/branches.html#delete-repository-branch
 func (s *BranchesService) DeleteBranch(pid interface{}, branch string, options ...OptionFunc) (*Response, error) {
 	project, err := parseID(pid)
 	if err != nil {
@@ -225,7 +223,7 @@ func (s *BranchesService) DeleteBranch(pid interface{}, branch string, options .
 // DeleteMergedBranches deletes all branches that are merged into the project's default branch.
 //
 // GitLab API docs:
-// https://gitlab.com/gitlab-org/gitlab-ce/blob/8-16-stable/doc/api/branches.md#delete-merged-branches
+// https://docs.gitlab.com/ce/api/branches.html#delete-merged-branches
 func (s *BranchesService) DeleteMergedBranches(pid interface{}, options ...OptionFunc) (*Response, error) {
 	project, err := parseID(pid)
 	if err != nil {