Allow opening a form to a route

This basically copies the Laravel Form route option, allowing for:

    {{ Former::open()->route('user.create') }}
    {{ Former::open()->route('user.update', [$user->id]) }}

Something I'd like to add is to set the form method to get/post based on the route but I'm not sure how to get that (perhaps need to get the route from the router manually).

PR is based off develop as [Contributing](https://github.com/Anahkiasen/former/blob/master/CONTRIBUTING.md) says to base off agnostic which isn't there :) Let me know if I should rebase onto master.