Update for Vapor 3.0

[paulyhedral]

Vapor 3 has a completely new model for serializable content and request routing, along with changes in Swift 4 that require some significant changes/updates to this code in order to make it work.

[koraykoska]

Hey @paulyhedral

You are right, there is certainly some amount of work we have to put into this to update it for Vapor 3. But unfortunately I don't have enough time right now to do this. I'm accepting pull requests though...