Vendor things

third-party/vendor/arc-swap/README.md

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+# ArcSwap
+
+[![Actions Status](https://github.com/vorner/arc-swap/workflows/test/badge.svg)](https://github.com/vorner/arc-swap/actions)
+[![codecov](https://codecov.io/gh/vorner/arc-swap/branch/master/graph/badge.svg?token=3KA3R2D9fV)](https://codecov.io/gh/vorner/arc-swap)
+[![docs](https://docs.rs/arc-swap/badge.svg)](https://docs.rs/arc-swap)
+
+This provides something similar to what `RwLock<Arc<T>>` is or what
+`Atomic<Arc<T>>` would be if it existed, optimized for read-mostly write-seldom
+scenarios, with consistent performance characteristics.
+
+Read [the documentation](https://docs.rs/arc-swap) before using.
+
+## Rust version policy
+
+The 1. version will build on any edition 2018 capable compiler. This does not
+include:
+
+* Tests. Tests build and run on recent compilers, mostly because of
+  dependencies.
+* Additional feature flags. Most feature flags are guaranteed to build since the
+  version they are introduced. Experimental features are without any guarantees.
+
+## License
+
+Licensed under either of
+
+ * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
+ * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
+
+at your option.
+
+### Contribution
+
+Unless you explicitly state otherwise, any contribution intentionally
+submitted for inclusion in the work by you, as defined in the Apache-2.0
+license, shall be dual licensed as above, without any additional terms
+or conditions.
+
+[`Arc`]: https://doc.rust-lang.org/std/sync/struct.Arc.html
+[`AtomicPtr`]: https://doc.rust-lang.org/std/sync/atomic/struct.AtomicPtr.html
+[`ArcSwap`]: https://docs.rs/arc-swap/*/arc_swap/type.ArcSwap.html