Add disabled? method on Flipper object

[dssjoblom]

A really small feature request: could you add the inverse of Flipper.enabled? that checks whether a feature is disabled. Right now you have to use boolean logic to check this.

[bkeepers]

Hi @dssjoblom. This has come up a few times in the past, most recently #494. Check out the discussion there and feel free to add to it.

[bkeepers]

I'm going to close this duplicate issue to keep things tidy around here.