Add an option to throw an exception or return instead of calling exit()

[d0x2f]

Calling exit aborts the entire application making it difficult work around in some situations, such as during unit tests or when the outcome of an invocation should be logged.

An option to throw an exception instead of calling exit would be great!

Relevant line: https://github.com/nategood/commando/blob/7ae153aa211c0686f139062856642e33bf8a86e0/src/Commando/Command.php#L460

[tolidano]

See my PHP 7.2+ fork/rewrite, which does neither: https://packagist.org/packages/tolidano/commandox

Happy to discuss further there.