Support for Rust 2018 edition

[ErichDonGubler]

It'd be nice if we could just add this to the embedded manifest and just be good to go, like with normal cargo manifests, once the new edition is out:

//! ```cargo
//! edition = "2018"
//! ...
//! ```

[theduke]

This works for me with:

//! ```cargo
//! [package]
//! edition = "2018"
//!
//! [dependencies]
//! ```

(Apart from the probably unrelated hanging issue #67 )

[ErichDonGubler]

Ahhh...my mistake was not using the [package] key header. It works for me! Thank you! :)

[Avi-D-coder]

The default should be edition = "2018"

[theduke]

Yeah it should, but considering that the last commit was on Oct 29, 2017, it is fair to say that this crate is unmaintained.

You can check out https://github.com/fanzeyi/cargo-play as an alternative.