Add tpl/site and tpl/hugo

This means that the current `.Site` and ´.Hugo` is available as a globals, so you can do `site.IsServer`, `hugo.Version` etc.

Fixes #5470
Fixes #5467
Fixes #5503

hugolib/template_test.go

@@ -236,3 +236,24 @@ Page Content
 	b.AssertFileContent("public/page/index.html", "Base: Hi!?")
 
 }
+
+func TestTemplateFuncs(t *testing.T) {
+
+	b := newTestSitesBuilder(t).WithDefaultMultiSiteConfig()
+
+	homeTpl := `Site: {{ site.Language.Lang }} / {{ .Site.Language.Lang }} / {{ site.BaseURL }}
+Hugo: {{ hugo.Generator }}
+`
+
+	b.WithTemplatesAdded(
+		"index.html", homeTpl,
+		"index.fr.html", homeTpl,
+	)
+
+	b.CreateSites().Build(BuildCfg{})
+
+	b.AssertFileContent("public/en/index.html", "Site: en / en / http://example.com/blog",
+		"Hugo: <meta name=\"generator\" content=\"Hugo")
+	b.AssertFileContent("public/fr/index.html", "Site: fr / fr / http://example.com/blog")
+
+}