Show dev-dependencies separately

[bluss]

Under dependencies for a crate, both dev-dependencies and dependencies are listed together.

It would be good to mark dev-dependencies separately: pulling in too many dependencies isn't always popular, and a crate's dev-dependencies do not become your own dependencies, when you use the crate, so they should be distinguished.

[spk]

This can be closed I guess its on production cf https://docs.rs/pyo3/0.6.0-alpha.4/pyo3/

[onur]

Yes, thank you @spk, sorry it took too long to review that PR.