Automate the Hugo release process

This commit adds a work flow aroung GoReleaser to get the Hugo release process automated and more uniform:

* It can be run fully automated or in two steps to allow for manual edits of the relase notes.
* It supports both patch and full releases.
* It fetches author, issue, repo info. etc. for the release notes from GitHub.
* The file names produced are mainly the same as before, but we no use tar.gz as archive for all Unix versions.
* There isn't a fully automated CI setup in place yet, but the release tag is marked in the commit message with "[ci deploy]"

Fixes #3358

releaser/github.go

@@ -0,0 +1,129 @@
+package releaser
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"os"
+)
+
+var (
+	gitHubCommitsApi      = "https://api.github.com/repos/spf13/hugo/commits/%s"
+	gitHubRepoApi         = "https://api.github.com/repos/spf13/hugo"
+	gitHubContributorsApi = "https://api.github.com/repos/spf13/hugo/contributors"
+)
+
+type gitHubCommit struct {
+	Author  gitHubAuthor `json:"author"`
+	HtmlURL string       `json:"html_url"`
+}
+
+type gitHubAuthor struct {
+	ID        int    `json:"id"`
+	Login     string `json:"login"`
+	HtmlURL   string `json:"html_url"`
+	AvatarURL string `json:"avatar_url"`
+}
+
+type gitHubRepo struct {
+	ID           int    `json:"id"`
+	Name         string `json:"name"`
+	Description  string `json:"description"`
+	HtmlURL      string `json:"html_url"`
+	Stars        int    `json:"stargazers_count"`
+	Contributors []gitHubContributor
+}
+
+type gitHubContributor struct {
+	ID            int    `json:"id"`
+	Login         string `json:"login"`
+	HtmlURL       string `json:"html_url"`
+	Contributions int    `json:"contributions"`
+}
+
+func fetchCommit(ref string) (gitHubCommit, error) {
+	var commit gitHubCommit
+
+	u := fmt.Sprintf(gitHubCommitsApi, ref)
+
+	req, err := http.NewRequest("GET", u, nil)
+	if err != nil {
+		return commit, err
+	}
+
+	err = doGitHubRequest(req, &commit)
+
+	return commit, err
+}
+
+func fetchRepo() (gitHubRepo, error) {
+	var repo gitHubRepo
+
+	req, err := http.NewRequest("GET", gitHubRepoApi, nil)
+	if err != nil {
+		return repo, err
+	}
+
+	err = doGitHubRequest(req, &repo)
+	if err != nil {
+		return repo, err
+	}
+
+	var contributors []gitHubContributor
+	page := 0
+	for {
+		page++
+		var currPage []gitHubContributor
+		url := fmt.Sprintf(gitHubContributorsApi+"?page=%d", page)
+
+		req, err = http.NewRequest("GET", url, nil)
+		if err != nil {
+			return repo, err
+		}
+
+		err = doGitHubRequest(req, &currPage)
+		if err != nil {
+			return repo, err
+		}
+		if len(currPage) == 0 {
+			break
+		}
+
+		contributors = append(contributors, currPage...)
+
+	}
+
+	repo.Contributors = contributors
+
+	return repo, err
+
+}
+
+func doGitHubRequest(req *http.Request, v interface{}) error {
+	addGitHubToken(req)
+
+	resp, err := http.DefaultClient.Do(req)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	if isError(resp) {
+		b, _ := ioutil.ReadAll(resp.Body)
+		return fmt.Errorf("GitHub lookup failed: %s", string(b))
+	}
+
+	return json.NewDecoder(resp.Body).Decode(v)
+}
+
+func isError(resp *http.Response) bool {
+	return resp.StatusCode < 200 || resp.StatusCode > 299
+}
+
+func addGitHubToken(req *http.Request) {
+	gitHubToken := os.Getenv("GITHUB_TOKEN")
+	if gitHubToken != "" {
+		req.Header.Add("Authorization", "token "+gitHubToken)
+	}
+}