Upgrade Tokio to version 0.3.0

[romac]

Implemented in: #681

Crates

rpc, light-client, light-node

Summary

Upgrade Tokio to version 0.3 to benefit from it's improved Runtime to facilitate integration of async tasks within sync code.

Problem Definition

The upcoming chain runtime in ibc-rs needs to bridge the gap between async and sync code.

The improved Runtime in Tokio 0.3 would help us implement a better chain runtime, thanks to its ability to be wrapped in an Arc, and shared between threads and components while still allowing to block_on futures.

This would also be useful for the light client: with Tokio 0.3, we can avoid spawning a new thread+runtime when blocking on each RPC request and instead have the Io component be parametrized with a Tokio Runtime.

Proposal

• Upgrade Tokio to version 0.3.
• Upgrade all dependencies which depends on Tokio 0.2 to newer versions for Tokio 0.3 support.
  • async-tungstenite: 0.8 => 0.10
  • hyper: 0.13 => 0.14.0-dev (development version)