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

tpl/template.go

@@ -94,6 +94,10 @@ func New() Template {
 
 	localTemplates = &templates.Template
 
+	// The URL funcs in the funcMap is somewhat language dependent,
+	// so need to be reinit per site.
+	initFuncMap()
+
 	for k, v := range funcMap {
 		amber.FuncMap[k] = v
 	}