Terminal exit codes.

The goal of this library is to provide human friendly and standard way to use exit status codes in command line applications. Instead of saying exit(64), you can say exit_with(:usage_error). Both indicate a failure to the parent process but the :usage_error is so much nicer! Wouldn't you agree? That's why tty-exit gathers a list of all the most common exit codes as used by POSIX-compliant tools on different Unix systems for you to use.