Blocks category for NSAlert/NSMenuItem

[indragiek]

I have these categories that add block support to NSAlert and NSMenuItem, and I was thinking they might be a good addition to Rebel if you guys think that this is within the scope of the problems the framework is designed to solve. Let me know if I should submit a PR.

[jspahrsummers]

👍

[jspahrsummers]

For future, by the way, please feel free to just submit a PR, even if you're not sure it will be accepted. Doing so reduces back-and-forth and makes it easier to discuss concretely.

[indragiek]

Will do.