Merge branch 'master' into jgrpp

# Conflicts:
#	src/error.h
#	src/error_gui.cpp
#	src/linkgraph/linkgraph_gui.cpp
#	src/misc_gui.cpp
#	src/newgrf_gui.cpp
#	src/news_gui.cpp
#	src/rail_cmd.cpp
#	src/saveload/gamelog_sl.cpp
#	src/script/api/script_text.cpp
#	src/script/script_instance.cpp
#	src/statusbar_gui.cpp
#	src/strings.cpp
#	src/strings_func.h
#	src/strings_internal.h
#	src/table/settings/gui_settings.ini
#	src/table/settings/linkgraph_settings.ini
#	src/textbuf_gui.h

src/settings_internal.h

@@ -246,6 +246,8 @@ struct BoolSettingDesc : IntSettingDesc {
 		PreChangeCheck pre_check, PostChangeCallback post_callback) :
 		IntSettingDesc(save, name, flags, guiproc, startup, patx_name, def, 0, 1, 0, str, str_help, str_val, cat, pre_check, post_callback, nullptr) {}
 
+	static std::optional<bool> ParseSingleValue(const char *str);
+
 	bool IsBoolSetting() const override { return true; }
 	size_t ParseValue(const char *str) const override;
 	void FormatIntValue(char *buf, const char *last, uint32 value) const override;