feat(EXCEPTIONS): custom exceptions to override default error handling

[niall-byrne]

I wanted to add some functionality that would let me override the default return to shell logic, in certain circumstances. (ie. when I press CTRL-BREAK on a spawned ansible process managed by this CLI, I wanted to exit the app and halt everything.).

I thought there might be other use cases for this, so I put together this feature. I hope it's useful.

(Great package, thanks!)

[niall-byrne]

Rebased with latest changes.

[niall-byrne]

Added documentation.

[niall-byrne]

I'm going to go with another solution.