`helper_method` was taking `**kwargs` on all definitions by default.
ruby will assume that this means you want keyword args and call
`to_hash` on what you pass if the object responds to `to_hash`. Instead
we should only take keyword args if the helper method defined intends
to pass keyword args.

This also fixes a warning when you pass a hash to your helper method,

```
warning: Using the last argument as keyword parameters is deprecated; maybe ** should be added to the call
```

Also, this would be a good candidate for using `...`, but since `send`
requires the method as the first argument, we can't use it here.