Add flags to include/exclude specific features

[cuviper]

In crates where I'm supporting older Rust versions, it's frequently the case that some of the features will only work on more recent Rust. So in order to use cargo all-features, I would need a way to list which features are actually expected to work for the Rust that I'm currently testing.

Another case is that many crates have features like "unstable" that would only be expected to work when using a nightly toolchain. That would need to be excluded when testing all stable features.

[frewsxcv]

Sounds good to me. I won't be able to get to this, so if someone wants to work on it, go ahead! Once you open a PR, I can review + merge + release

[Person-93]

Sounds good to me. I won't be able to get to this, so if someone wants to work on it, go ahead! Once you open a PR, I can review + merge + release

You said here that you want to keep the flags the same as cargo, so maybe something like this?
cargo all-features <ALL_FEATURES_ARGUMENTS> [-- <CARGO_ARGUMENTS>]
Or this?
cargo all-features <CARGO_COMMAND> [ALL_FEATURES_ARGUMENTS] [-- <CARGO_ARGUMENTS>]

[demmerichs]

I think this issue can be closed as at least some configurability through Cargo.toml is given. More explicit feature requests should be covered in a new issue.