Conditional behavior in debug/release mode for cxx::Expects and cxx::Ensures

## Brief feature description

Add conditional behavior on debug/release mode for `cxx::Expects` and `cxx::Ensures`.

## Detailed information

Current state is that `cxx::Expects` and `cxx::Ensures` terminate if the condition is not met.
Suggestion to add conditional behavior on debug/release mode for both functions, like in debug mode you will be terminated with a detailed error message and in release mode we continue.

Optional/to be discussed:
- Add a parameter allowing continuation, e. g.:
```
cxx::Expects( myNumber > 0 ); // hard, calls std::terminate always
cxx::Expects( myNumber > 0, ALGORITHM_CAN_CONTINUE); // we can continue even the requirement is not fulfilled
```
- Can there be a `constexpr` version of `cxx::Expects` and `cxx::Ensures`?