Configure `features` per target platform

[frol]

I am an early user of cargo-dist, and I love it!

It would be great to be able to configure features per target as some of the platforms do not support one thing or another. For example, I don't want to build udev-dependent code for linux-musl-static builds, so I would just disable default-features and enable only the features that make sense for musl-static build.

I wish cargo support it, and then cargo-dist may not need to implement it: https://github.com/rust-lang/cargo/issues/1197