Add libiconv support

str_util.h

@@ -0,0 +1,13 @@
+#ifndef _UTILS_STR_UTIL_H
+#define _UTILS_STR_UTIL_H
+#include <string>
+namespace str_util {
+    /**
+     * @brief Convert string to lowercase
+     * @param ori Origin string
+     * @param result Output string.
+     * @return true if successed.
+    */
+    bool tolowercase(std::string ori, std::string& result);
+}
+#endif