C++20 base

Allow C++20 compilation standard and add minimal changes needed to compile the project.

CMake/CompilerFlags.cmake

@@ -7,7 +7,7 @@ if(NOT ${CMAKE_CXX_COMPILER_ID} MATCHES "(Clang|GNU)")
 endif ()
 set(CMAKE_CXX_STANDARD 20)
-add_compile_options(-Wno-ambiguous-reversed-operator) #FIXME warning in compare operators class that is supposed to be removed after finally switching to C++20
+add_compile_options(-Wno-ambiguous-reversed-operator) #FIXME warning in compare operators class that is supposed to be removed after the transition to C++20 three way comparison is finished
 set(CXX_STANDARD_REQUIRED ON)
 set(CMAKE_POSITION_INDEPENDENT_CODE ON)