work on settings (set and show), perf improvement when adding row into table

settings.h

@@ -8,12 +8,12 @@ namespace usql {
 class Settings {
 
 public:
+    static void set_setting(const std::string &name, const std::string &value);
+    static std::string get_setting(const std::string &name);
+
     static long string_to_date(const std::string &datestr);
     static std::string date_to_string(long date);
 
-private:
-    static std::basic_string<char> get_setting(const std::string &name);
-
 private:
     static std::vector<std::pair<std::string, std::string>> m_settings;
 };