Vendor dependencies

Let's see how I like this workflow.

vendor/redox_users/README.md

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+# redox_users <a href="https://crates.io/crates/redox_users"><img src="https://img.shields.io/crates/v/redox_users.svg"></a>
+
+Redox OS APIs for accessing users and groups information. [Documentation](https://docs.rs/redox_users/0.1.0/redox_users/)
+
+High level APIs for:
+
+- Getting the current process effective user ID.
+- Getting the current process user ID.
+- Getting the current process effective group ID.
+- Getting the current process group ID.
+- Manipulating User and Group information (including adding, removing, and modifying groups and users, in addition to other functionality, see docs)
+
+We recommend to use these APIs instead of directly manipulating the
+`/etc/group` and `/etc/passwd` as this is an implementation detail and
+might change in the future.
+
+Note that redox_users is an API designed only for use on Redox. It compiles on other platforms (for testing), but it will not work and might produce unexpected behavior.
+
+## Hashing
+redox_users uses the Argon2 hashing algorithm. The default hashing parameters are as follows:
+```Rust
+Argon2::new(10, 1, 4096, Variant::Argon2i)
+```