Create a template system for the graphite serializer

closes #925
closes #879

internal/config/config.go

@@ -850,8 +850,17 @@ func buildSerializer(name string, tbl *ast.Table) (serializers.Serializer, error
 		}
 	}
 
+	if node, ok := tbl.Fields["template"]; ok {
+		if kv, ok := node.(*ast.KeyValue); ok {
+			if str, ok := kv.Value.(*ast.String); ok {
+				c.Template = str.Value
+			}
+		}
+	}
+
 	delete(tbl.Fields, "data_format")
 	delete(tbl.Fields, "prefix")
+	delete(tbl.Fields, "template")
 	return serializers.NewSerializer(c)
 }