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

tpl/site/init.go

@@ -0,0 +1,44 @@
+// Copyright 2018 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 site
+
+import (
+	"github.com/gohugoio/hugo/deps"
+
+	"github.com/gohugoio/hugo/tpl/internal"
+)
+
+const name = "site"
+
+func init() {
+	f := func(d *deps.Deps) *internal.TemplateFuncsNamespace {
+
+		s := d.Site
+		ns := &internal.TemplateFuncsNamespace{
+			Name:    name,
+			Context: func(args ...interface{}) interface{} { return s },
+		}
+
+		if s == nil {
+			panic("no Site")
+		}
+
+		// We just add the Site as the namespace here. No method mappings.
+
+		return ns
+
+	}
+
+	internal.AddTemplateFuncsNamespace(f)
+}