Remove shiftnums as they are incompatible with international keyboards

The usage of `shiftNums` to allow bindings such as `$` to indicate `Shift+4` don't work on non-US keyboard layouts.

**French keyboard**
![38565_xlargenss_ndo4211](https://cloud.githubusercontent.com/assets/201344/3985799/3c35da74-2895-11e4-95c1-d159ecd71b9e.jpg)

As you can see, the $ key is a dedicated key next to return. Binding to `$` won't actually trigger when you press the $ key, as it has keycode 220.

This issue with jquery.hotkeys was noted over two years ago https://github.com/ccampbell/mousetrap/issues/2#issuecomment-6818461, but since this repo doesn't have issues, it went unreported.

Removing this feature is not a complete fix for this problem, but I wanted to raise the issue in the form of a pull request so it's documented that this is a problem with this jQuery plugin.