improve support for cargo workspaces

[0xalpharush]

I am getting an error like Error: package '/Users/alpharush/tob/../Cargo.toml' is a member of the wrong workspace. Can we improve support for cargo workspaces?

Probably relevant to the fix:

siderophile/src/main.rs

Lines 41 to 67 in debb857

	let config = cargo::Config::default()?;
	let workspace_root = cargo::util::important_paths::find_root_manifest_for_wd(config.cwd())?;
	let ws = cargo::core::Workspace::new(&workspace_root, &config)?;
	let mut ws = if let Some(name) = &args.package {
	let package =
	find_package(&ws, name).ok_or_else(|| anyhow!("Could not find package `{}`", name))?;
	Workspace::ephemeral(package.clone(), &config, None, false)?
	} else {
	ws
	};
	let tempdir = tempdir_in(config.cwd())?;
	ws.set_target_dir(Filesystem::new(tempdir.path().to_path_buf()));
	let crate_name = crate_name(&ws, &args.package)?;
	if let Some(deprecated_crate_name) = &args.crate_name {
	eprintln!("Warning: `--crate-name` is deprecated. Use `--package` instead.");
	if deprecated_crate_name != &crate_name {
	bail!(
	"Crate `{}` was specified, but crate `{}` was found",
	deprecated_crate_name,
	crate_name
	);
	}
	}

Maybe related to #31