Add string() method as an alias for str(), which is defined in STL.

Author: tatsy

filesystem/path.h

@@ -225,6 +225,10 @@ class path {
         return oss.str();
     }
 
+    std::string string() const {
+        return str();
+    }
+
     void set(const std::string &str, path_type type = native_path) {
         m_type = type;
         if (type == windows_path) {