Refactor then to async functions

[fson]

Replace all uses of Promise#then with async functions.

[freiksenet]

Can't comment on lines from phone, but why do you need to await on close connection? Why not just return it?

Fine otherwise.

[fson]

closeConnection is called on the tail event which is emitted after the response has been sent.

It seemed more prudent to await in case there's an error, but I guess that does not matter because the promise returned by this function is discarded anyway. 😄 An error would probably still bubble up to Bluebird's global handler that logs it in the console...

So I think it does not make any difference.

[fson]

I've removed the await on conn.close(). This matches the previous behaviour with promises. Also maybe it makes it clearer that we discard the result.

[freiksenet]

There is no difference between explicit await at the end of function and returning a promise. But it is confusing IMO, can be misinterpreted, please remove it.

[freiksenet]

Thanks. Shipit.