keybinder-3.0: Add package

Does the naming scheme (`keybinder_3_0`) seem reasonable?
> I guess it should be name = "keybinder-3.0-${version}" (3.0 instead of 0.3)?

Yes, it looks the similarity between the API version (3.0) and the release version (0.3.0) bit me, and I accidentally transposed the 3 and 0. I'll fix this up real quick.