respect rails 5 `assigns` render option
respect rails 5 `assigns` render option

Rails 5 supports an `assigns` option to `render`/`render_to_string` that allows setting instance variables available to the template. This is particularly handy for rendering outside of controllers where these instance variables wouldn't otherwise be available.

It's a pass-through so I didn't add any new tests (but could.)

mileszs/wicked_pdf,bonekost/wicked_pdf