allow actions to have an array of middleware which express calls before calling action

Don't know if this is something ya'll will support or merge, but I wanted to highlight it even so in case you have a recommended alternative solution. I often have multiple middleware functions in my Express routes ([example](https://github.com/HabitRPG/habitrpg/blob/2f4112e2f110790ea6750a2d743b18f4aab283bc/src/routes/apiv2.js#L119)). swagger-node-express handles the case of *one* common middleware being authentication, but not multiple. Of course, I could use `async.waterfall` in the `action` property - which I started to do, but which got unwieldy. This PR might be a decent/clean approach.