Avoid reading from Viper for path and URL funcs

The gain, given the "real sites benchmark" below, is obvious:

```
benchmark           old ns/op       new ns/op       delta
BenchmarkHugo-4     14497594101     13084156335     -9.75%

benchmark           old allocs     new allocs     delta
BenchmarkHugo-4     57404335       48282002       -15.89%

benchmark           old bytes       new bytes      delta
BenchmarkHugo-4     9933505624      9721984424     -2.13%
```

Fixes #2495

helpers/pathspec.go

@@ -0,0 +1,54 @@
+// Copyright 2016-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 helpers
+
+// PathSpec holds methods that decides how paths in URLs and files in Hugo should look like.
+type PathSpec struct {
+	disablePathToLower bool
+	removePathAccents  bool
+	uglyURLs           bool
+	canonifyURLs       bool
+
+	currentContentLanguage *Language
+
+	// pagination path handling
+	paginatePath string
+
+	// The PathSpec looks up its config settings in both the current language
+	// and then in the global Viper config.
+	// Some settings, the settings listed below, does not make sense to be set
+	// on per-language-basis. We have no good way of protecting against this
+	// other than a "white-list". See language.go.
+	defaultContentLanguageInSubdir bool
+	defaultContentLanguage         string
+	multilingual                   bool
+}
+
+func NewPathSpecFromConfig(config ConfigProvider) *PathSpec {
+	return &PathSpec{
+		disablePathToLower:             config.GetBool("disablePathToLower"),
+		removePathAccents:              config.GetBool("removePathAccents"),
+		uglyURLs:                       config.GetBool("uglyURLs"),
+		canonifyURLs:                   config.GetBool("canonifyURLs"),
+		multilingual:                   config.GetBool("multilingual"),
+		defaultContentLanguageInSubdir: config.GetBool("defaultContentLanguageInSubdir"),
+		defaultContentLanguage:         config.GetString("defaultContentLanguage"),
+		currentContentLanguage:         config.Get("currentContentLanguage").(*Language),
+		paginatePath:                   config.GetString("paginatePath"),
+	}
+}
+
+func (p *PathSpec) PaginatePath() string {
+	return p.paginatePath
+}