Set Rust Language Edition (2021) for the project Cargo.toml

[evan0greenup]

Currently, the language edition is not set, when run cargo build, cargo will choose edition 2015 if the language edition is not explicitly set.

It would be nice to set it to 2021 in the project Cargo.toml file.

[daniel-levin]

#152

[evan0greenup]

@daniel-levin , why this PR not merge?

[daniel-levin]

Probably because it's a large change (in the sense that it touches many files) by a new contributor and it's the holiday season. In the new year I'll ping the maintainers.

[daniel-levin]

@evan0greenup heads up that #152 is merged, you can close this issue.