Trait Termination

A trait for implementing arbitrary return types in the main function.

The C-main function only supports returning integers. So, every type implementing the Termination trait has to be converted to an integer.

The default implementations are returning libc::EXIT_SUCCESS to indicate a successful execution. In case of a failure, libc::EXIT_FAILURE is returned.

Because different runtimes have different specifications on the return value of the main function, this trait is likely to be available only on standard library's runtime for convenience. Other runtimes are not required to provide similar functionality.