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/genman.go

@@ -36,7 +36,7 @@ in the "man" directory under the current directory.`,
 		header := &doc.GenManHeader{
 			Section: "1",
 			Manual:  "Hugo Manual",
-			Source:  fmt.Sprintf("Hugo %s", helpers.HugoVersion()),
+			Source:  fmt.Sprintf("Hugo %s", helpers.CurrentHugoVersion),
 		}
 		if !strings.HasSuffix(genmandir, helpers.FilePathSeparator) {
 			genmandir += helpers.FilePathSeparator