Vendor dependencies

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vendor/signal-hook-registry/README.md

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+# Signal-hook-registry
+
+[![Travis Build Status](https://api.travis-ci.org/vorner/signal-hook.svg?branch=master)](https://travis-ci.org/vorner/signal-hook)
+
+This is the backend crate for the
+[signal-hook](https://crates.io/crates/signal-hook) crate. The general direct use of
+this crate is discouraged. See the
+[documentation](https://docs.rs/signal-hook-registry) for further details.
+
+## 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.