C++14 compiler compatibility
Updated test run scripts
Changed some ETL_ASSERT macros to ETL_ASSERT_OR_RETURN
Changed unit test macros for C++20 compaibility
Updated test run scripts
Updated CMake files to allow C++ standard selection
Replaced ETL_ASSERT_AND_RETURN with ETL_ASSERT_OR_RETURN
Updated C++14 & C++20 unit test compatibility
Changed native char8_t check
Added optional optimisation argument to bash script
In order to work properly, states with no change need to return ifsm_state::NO_CHANGE rather than their given state id.
Otherwise, when an event isn't handled, it will return the parent state rather than the active state.
Also, in this implementation, a state cannot return a different state during the on_enter_state() function. An assert has been added to check for that.
