Fix Params case handling in the index, sort and where func

This means that you can now do:

```
{{ range where .Site.Pages "Params.MYPARAM" "foo" }}
```

langs/config.go

@@ -171,7 +171,7 @@ func toSortedLanguages(cfg config.Provider, l map[string]interface{}) (Languages
 	i := 0
 
 	for lang, langConf := range l {
-		langsMap, err := cast.ToStringMapE(langConf)
+		langsMap, err := maps.ToStringMapE(langConf)
 
 		if err != nil {
 			return nil, fmt.Errorf("Language config is not a map: %T", langConf)
@@ -192,7 +192,7 @@ func toSortedLanguages(cfg config.Provider, l map[string]interface{}) (Languages
 			case "disabled":
 				language.Disabled = cast.ToBool(v)
 			case "params":
-				m := cast.ToStringMap(v)
+				m := maps.ToStringMap(v)
 				// Needed for case insensitive fetching of params values
 				maps.ToLower(m)
 				for k, vv := range m {