Refactor middleware

[blakeembrey]

Using before, after and always is kind of tricky and there are a couple of edge-cases. Middleware could be better served with a slightly different paradigm - make middleware just a function call that wraps the request. In a way, the request starts to look more like async middleware. We could probably even re-create Koa-like interfaces.

function retry (next: Function) {
  var ctx = this

  return next()
    .then(function () {
      if (ctx.response.type() === 5) {
        return new popsicle.Request(ctx.options())
      }
    }, function (err) {
      if (err.code === 'EUNAVAILABLE') {
        return new popsicle.Request(ctx.options())
      }

      return Promise.reject(err)
    })
}