add async await syntax support to Router

[logig]

add async await error handle support to Router.

[wesleytodd]

Hey @logig! Thanks for your contribution. I think it might be a bit more complicated than this PR makes it out to be. To get async/await support we need more than just this change, and there has been some work done on this which you might want to check out:

#2259
pillarjs/router#60

Lastly, it would be great if you want to take up this project, but you would want to do it on the router repo linked above, as that is what express@5 will be using.

[logig]

Got it.