tpl: Add some GoDoc info to template func docs

Closes #3418

tpl/cast/cast.go

@@ -26,10 +26,12 @@ func New() *Namespace {
 type Namespace struct {
 }
 
+// ToInt converts the given value to an int.
 func (ns *Namespace) ToInt(v interface{}) (int, error) {
 	return _cast.ToIntE(v)
 }
 
+// ToString converts the given value to a string.
 func (ns *Namespace) ToString(v interface{}) (string, error) {
 	return _cast.ToStringE(v)
 }

tpl/cast/docshelper.go

@@ -25,7 +25,7 @@ func init() {
 		docs := make(map[string]interface{})
 		d := &deps.Deps{}
 
-		var namespaces []*internal.TemplateFuncsNamespace
+		var namespaces internal.TemplateFuncsNamespaces
 
 		for _, nsf := range internal.TemplateFuncsNamespaceRegistry {
 			nf := nsf(d)