Add support for desktop notifications

[axcdnt]

Is your feature request related to a problem? Please describe.
A clear way to enable/disable desktop notifications. Sometimes I'm on my editor, away from the terminal and that would be nice.

Describe the solution you'd like
A support for multiple OSes by showing a minimal (title, failures, successes) desktop notifications. This could be enabled/disabled via params. I don't think a yaml or something like would add much.

I don't think there is a simple way to count successes and failures, but this could be parsed from
stdout at the cost of adding a delay before showing the notification.