Proposal: Removal of support for callbacks

[wjhsf]

Development of tough-cookie began in 2011. Back then, callbacks were the standard pattern for handling async behavior. (Promises were around, but not yet standardized.) In the decade since, a lot has changed in the world of JavaScript. In particular, promises have replaced callbacks as the popular way of doing async. To that end, to simplify the tough-cookie code base, we are considering removing support for callbacks, and only providing a promise-based API. As a breaking change, this would be done in a new major release of the package.

We recognize that tough-cookie is very widely used, so we are seeking community feedback to understand how our package is used before making a decision.