update tokio to 0.2

[12101111]

This allow us to use std::future and async/await

Changes:

• bumped tokio to 0.2 (use master branch for now)
• bumped futures 0.1 to futures-preview 0.3
• use rust 2018 edition

Block for stabilization:

• async/await stable in rust 1.39
• tokio release 0.2
• futures release 0.3

Related:
tokio-rs/tokio#1297
tokio-rs/tokio#1272
tokio-rs/tokio#1225 (examples)

[berkowski]

Thanks for starting this! I somehow missed qm3ster's issue. I've got a lot of catching up to do with tokio to get back up to speed. I'll do some reading up and look over what you've started in the next couple days.

[berkowski]

Finally had some time to look into this and your PR. Sorry, I should have gotten around to it much sooner!

Your solution works well, but I am not going to merge it into master just yet as tokio 0.2 and futures 0.3 haven't landed. However, I would still like to provide an 'alpha' style package on crates.io for those users that want to take advantage of async/await.

To that end I've made a new branch (tokio-0.2.0-alpha.1) and intend to push a release to crates.io. I want to give you credit though, so let me know which would work for you:

1. I create a new empty branch for you to retarget your merge to and publish after some cleanup.
2. I publish the new branch as is and credit you in the changelog

[berkowski]

Closing this now. I've gone ahead and pushed a release to crates.io incorporating tokio-0.2 support as it stands currently. Thanks for your work on this, I've added you and others to the changelog notes.