Stripe: Add a pay-per-article option

This would be especially helpful for me. You could think of it as pay-as-you-go, basically just an addition to the subscription options.

The use case:
I write long-form articles explaining complex topics. The topics covered are hard to find much good information on, so users are willing to pay. BUT…

If my output is ~1 article per month, then I think the consumer would be much happier with this option.