title: Stripe subscription with fixed renewal date
body: <p>I want to use Stripe subscriptions to handle a membership fee. The issue is that memberships are annual, and they cost a fixed amount, no matter when you sign up. I.e. you're paying for the full period even if they sign up in the middle of the period.</p>
  <p>So for example let's say that a membership costs $100, and it runs from Jan 1 to Dec 31. If someone signs up today, they should get an invoice for $100, and then the subscription should be renewed for another $100 on Jan 1.</p>
  <p>I've experimented a bit with creating the subscription using the <code>backdate_start_date</code>, <code>billing_cycle_anchor</code>, and <code>proration_behavior</code> fields, but haven't really gotten it to work quite as I would like it to.</p>
  <p>Has anyone gotten a scenario like this working? Or any idea of how to best manage this?</p>