`rimd` library is now fairly out of date with respect to modern Rust style -- let's fix that

[akesling]

Running cargo clippy provides the following output : https://gist.github.com/akesling/4535958548c362d09d52fa5c86c24f23

I propose fixing these issues.

[Boscop]

It also uses the old num-derive 0.2 which gives me an error when another dep depends on 0.3 :/

[akesling]

Great suggestion @Boscop. I've created a pull request for that update: #19