Upgrade to Rust 2018 and latest hyper with tokio

[david-perez]

I wanted to try this out since I am in need of such a tool and was greeted with this compilation error as a result of the outdated hyper-native-tls dependency which is incompatible with the OpenSSL 1.1 I have in my system.

I decided to take it upon myself to make the project build again by updating hyper to its latest version and using hyper-tls instead, so much of the code has had to be rewritten with async/await (using tokio) in mind, a Rust 2018 edition feature.

I've tested out all the binaries manually with these changes to make sure I didn't break anything; they seem to be working well.

[david-perez]

Cross-compiling openssl-sys seems to be tricky. I don't know why it fails.

Let's try rustls.

[bltavares]

Thank you :)