Add support for multiple staticDirs

This commit adds support for multiple statDirs both on the global and language level.

A simple `config.toml` example:

```bash
staticDir = ["static1", "static2"]
[languages]
[languages.no]
staticDir = ["staticDir_override", "static_no"]
baseURL = "https://example.no"
languageName = "Norsk"
weight = 1
title = "På norsk"

[languages.en]
staticDir2 = "static_en"
baseURL = "https://example.com"
languageName = "English"
weight = 2
title = "In English"
```

In the above, with no theme used:

the English site will get its static files as a union of "static1", "static2" and "static_en". On file duplicates, the right-most version will win.
the Norwegian site will get its static files as a union of "staticDir_override" and "static_no".

This commit also concludes the Multihost support in #4027.

Fixes #36
Closes #4027

tpl/urls/init_test.go

@@ -18,6 +18,7 @@ import (
 
 	"github.com/gohugoio/hugo/deps"
 	"github.com/gohugoio/hugo/tpl/internal"
+	"github.com/spf13/viper"
 	"github.com/stretchr/testify/require"
 )
 
@@ -26,7 +27,7 @@ func TestInit(t *testing.T) {
 	var ns *internal.TemplateFuncsNamespace
 
 	for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
-		ns = nsf(&deps.Deps{})
+		ns = nsf(&deps.Deps{Cfg: viper.New()})
 		if ns.Name == name {
 			found = true
 			break

tpl/urls/urls.go

@@ -26,13 +26,15 @@ import (
 // New returns a new instance of the urls-namespaced template functions.
 func New(deps *deps.Deps) *Namespace {
 	return &Namespace{
-		deps: deps,
+		deps:      deps,
+		multihost: deps.Cfg.GetBool("multihost"),
 	}
 }
 
 // Namespace provides template functions for the "urls" namespace.
 type Namespace struct {
-	deps *deps.Deps
+	deps      *deps.Deps
+	multihost bool
 }
 
 // AbsURL takes a given string and converts it to an absolute URL.
@@ -109,7 +111,7 @@ func (ns *Namespace) RelLangURL(a interface{}) (template.HTML, error) {
 		return "", err
 	}
 
-	return template.HTML(ns.deps.PathSpec.RelURL(s, true)), nil
+	return template.HTML(ns.deps.PathSpec.RelURL(s, !ns.multihost)), nil
 }
 
 // AbsLangURL takes a given string and converts it to an absolute URL according
@@ -121,5 +123,5 @@ func (ns *Namespace) AbsLangURL(a interface{}) (template.HTML, error) {
 		return "", err
 	}
 
-	return template.HTML(ns.deps.PathSpec.AbsURL(s, true)), nil
+	return template.HTML(ns.deps.PathSpec.AbsURL(s, !ns.multihost)), nil
 }