Added `withKeyCode` option to action helper

For actions that are fired on `keyUp`, `keyDown` or `keyPress` an option called `withKeyCode` is now available to use. It ensures that the action is called only when the given `withKeyCode` value matches the keyCode on the event.

For example:

    <input type='text' {{action 'show' on='keyUp' withKeyCode='13'}}>

This action will only fire if the event is a `keyup` and the `keyCode` is 13.

This commit was done with help from: @tonycoco
Sorry to nit-pick, but we would usually have the prefix be the package name.  Could you change this to `ember-routing-handlebars-action-with-key-code` (and yes, that is insanely long)?