Allow deleting subscriptions with options

[williamhogman]

Useful for ending subscriptions on the next billing date, see https://stripe.com/docs/api#cancel_subscription

[williamhogman]

Thanks for the quick response :)

Yes, it encapsulated the incorrect assumption that DELETE methods cannot have request bodies. If a delete request did have a body it would be silently ignored and not passed on to HTTPPoison, which made my code really hard to debug. I think it is more sensible to let the upstream library figure out what is correct HTTP and for us to put a thin wrapper around it managing authentication.

[robconery]

Ahhh - that would make sense and yeah, I didn't catch that last part :) thanks!