keybinder-3.0: Add package

Does the naming scheme (`keybinder_3_0`) seem reasonable?
@lethalman  IIRC, something weird was going on, like github setting the Content-Disposition header and setting the filename sans .tar.gz extension, thus confusing the unpack phase. That sounds ridiculous, so that might not be quite right... can't remember.

At any rate, I'll just update this to use `fetchFromGitHub`.