add xml library

src/coders/xml.cpp

@@ -528,3 +528,11 @@ std::string xml::stringify(
 
     return ss.str();
 }
+
+std::string xml::stringify(
+    const Node& element, bool nice, const std::string& indentStr
+) {
+    std::stringstream ss;
+    stringifyElement(ss, element, nice, indentStr, 0);
+    return ss.str();
+}

src/coders/xml.hpp

@@ -119,6 +119,12 @@ namespace xml {
         const std::string& indentStr = "    "
     );
 
+    std::string stringify(
+        const Node& element,
+        bool nice = true,
+        const std::string& indentStr = "    "
+    );
+
     /// @brief Read XML Document from string
     /// @param filename file name will be shown in error messages
     /// @param source xml source code string