Vendor things

third-party/vendor/hashlink/README.md

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+# hashlink -- HashMap-like containers that hold their key-value pairs in a user controllable order
+
+[![Build Status](https://img.shields.io/circleci/project/github/kyren/hashlink.svg)](https://circleci.com/gh/kyren/hashlink)
+[![Latest Version](https://img.shields.io/crates/v/hashlink.svg)](https://crates.io/crates/hashlink)
+[![API Documentation](https://docs.rs/hashlink/badge.svg)](https://docs.rs/hashlink)
+
+This crate is a fork of 
+[linked-hash-map](https://github.com/contain-rs/linked-hash-map) that builds on
+top of [hashbrown](https://github.com/rust-lang/hashbrown) to implement more up
+to date versions of `LinkedHashMap` `LinkedHashSet`, and `LruCache`.
+
+One important API change is that when a `LinkedHashMap` is used as a LRU cache,
+it allows you to easily retrieve an entry and move it to the back OR produce a
+new entry at the back without needlessly repeating key hashing and lookups:
+
+``` rust
+let mut lru_cache = LinkedHashMap::new();
+let key = "key".to_owned();
+// Try to find my expensive to construct and hash key
+let _cached_val = match lru_cache.raw_entry_mut().from_key(&key) {
+    RawEntryMut::Occupied(mut occupied) => {
+        // Cache hit, move entry to the back.
+        occupied.to_back();
+        occupied.into_mut()
+    }
+    RawEntryMut::Vacant(vacant) => {
+        // Insert expensive to construct key and expensive to compute value,
+        // automatically inserted at the back.
+        vacant.insert(key.clone(), 42).1
+    }
+};
+```
+
+Or, a simpler way to do the same thing:
+
+``` rust
+let mut lru_cache = LinkedHashMap::new();
+let key = "key".to_owned();
+let _cached_val = lru_cache
+    .raw_entry_mut()
+    .from_key(&key)
+    .or_insert_with(|| (key.clone(), 42));
+```
+
+This crate contains a decent amount of unsafe code from handling its internal
+linked list, and the unsafe code has diverged quite a lot from the original
+`linked-hash-map` implementation.  It currently passes tests under miri and
+sanitizers, but it should probably still receive more review and testing, and
+check for test code coverage.
+
+## Credit
+
+There is a huge amount of code in this crate that is copied verbatim from
+`linked-hash-map` and `hashbrown`, especially tests, associated types like
+iterators, and things like `Debug` impls.
+
+## License
+
+This library is licensed the same as
+[linked-hash-map](https://github.com/contain-rs/linked-hash-map) and
+[hashbrown](https://github.com/rust-lang/hashbrown), it is licensed under either
+of:
+
+* MIT license [LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT
+* Apache License 2.0 [LICENSE-APACHE](LICENSE-APACHE) or https://opensource.org/licenses/Apache-2.0
+
+at your option.