Enable C++20 and use cmake 4

CMakeLists.txt

@@ -2,7 +2,7 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at https://mozilla.org/MPL/2.0/.
 
-cmake_minimum_required(VERSION 3.21)
+cmake_minimum_required(VERSION 4.0)
 project(Katja)
 
 include(CTest)
@@ -10,7 +10,8 @@ include(FetchContent)
 
 set(CMAKE_EXPORT_COMPILE_COMMANDS 1)
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
-set(CMAKE_CXX_STANDARD 17)
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_MODULE_STD 1)
 
 add_library(katja
        katja/database.cpp include/katja/database.hpp