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

commands/release.go

@@ -0,0 +1,62 @@
+// +build release
+
+// Copyright 2017-present The Hugo Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package commands
+
+import (
+	"github.com/spf13/cobra"
+	"github.com/spf13/hugo/releaser"
+)
+
+func init() {
+	HugoCmd.AddCommand(createReleaser().cmd)
+}
+
+type releaseCommandeer struct {
+	cmd *cobra.Command
+
+	// Will be zero for main releases.
+	patchLevel int
+
+	skipPublish bool
+
+	step int
+}
+
+func createReleaser() *releaseCommandeer {
+	// Note: This is a command only meant for internal use and must be run
+	// via "go run -tags release main.go release" on the actual code base that is in the release.
+	r := &releaseCommandeer{
+		cmd: &cobra.Command{
+			Use:    "release",
+			Short:  "Release a new version of Hugo.",
+			Hidden: true,
+		},
+	}
+
+	r.cmd.RunE = func(cmd *cobra.Command, args []string) error {
+		return r.release()
+	}
+
+	r.cmd.PersistentFlags().IntVarP(&r.patchLevel, "patch", "p", 0, "Patch level, defaults to 0 for main releases")
+	r.cmd.PersistentFlags().IntVarP(&r.step, "step", "s", -1, "Release step, defaults to -1 for all steps.")
+	r.cmd.PersistentFlags().BoolVarP(&r.skipPublish, "skip-publish", "", false, "Skip all publishing pipes of the release")
+
+	return r
+}
+
+func (r *releaseCommandeer) release() error {
+	return releaser.New(r.patchLevel, r.step, r.skipPublish).Run()
+}