macOS implementation

[SamuelMarks]

Inspiration by this MIT licensed C project - https://github.com/zserge/tray

(if I get the time I can contribute, otherwise just leaving it as an issue here as a feature request)

Thanks

[Curve]

Yes I really have to get that working.
I'll get to it in a bit

[Curve]

It will take me longer as expected, I still have some stuff to do - I'll install a VM next week and try to get everything working on macOS.

[hrnozel]

Do you have time to add this feature for macOS? If you don't, I can implement it for you?

[Curve]

I'm not experienced with macos development and don't have a machine to test / develop it on so I would actually be grateful for a PR ^^

[hrnozel]

I actually have no experience with osX :D, but I think I can do this with the objc runtime wrappers. I'll let you know here when I start.