[REQ] Upgrade to tokio 0.2 and related async/await features

Created by: dbcfd

Is your feature request related to a problem? Please describe.

The tokio ecosystem is currently migrating to std::future::Future and async/await support. This should land in rust 1.39 (currently stable in nightly)

Describe the solution you'd like

Upgrade to appropriate versions for tokio and hyper that make use of std::future::Future and async/await

Describe alternatives you've considered

Tokio 0.2 is not compatible with older hyper versions (pre hyper 0.13). One possibility is to try and use runtime and tide, but that is significantly more of a change.