Termination-related feedback

[Enyium]

• The readme should mention that the other process is terminated forcefully.
• When recommending std::mem::forget() or documenting a function that calls process::exit(), it would be good to mention that this will prevent destructors (Drop implementations) from running.
• The TerminateProcess() docs say: "If you need to be sure the process has terminated, call the WaitForSingleObject function with a handle to the process." That should probably be done. After a timeout of a couple of seconds, the waiting process could exit with an error message and error code 1 (or ExitCode::FAILURE if that type would be usable).