Initial import of x509-parser 0.9.2

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+<!-- cargo-sync-readme start -->
+
+[![License: MIT](https://img.shields.io/badge/License-MIT-yellow.svg)](./LICENSE-MIT)
+[![Apache License 2.0](https://img.shields.io/badge/License-Apache%202.0-blue.svg)](./LICENSE-APACHE)
+[![docs.rs](https://docs.rs/x509-parser/badge.svg)](https://docs.rs/x509-parser)
+[![crates.io](https://img.shields.io/crates/v/x509-parser.svg)](https://crates.io/crates/x509-parser)
+[![Download numbers](https://img.shields.io/crates/d/x509-parser.svg)](https://crates.io/crates/x509-parser)
+[![Github CI](https://github.com/rusticata/x509-parser/workflows/Continuous%20integration/badge.svg)](https://github.com/rusticata/x509-parser/actions)
+[![Minimum rustc version](https://img.shields.io/badge/rustc-1.45.0+-lightgray.svg)](#rust-version-requirements)
+
+# X.509 Parser
+
+A X.509 v3 ([RFC5280]) parser, implemented with the [nom](https://github.com/Geal/nom)
+parser combinator framework.
+
+It is written in pure Rust, fast, and makes extensive use of zero-copy. A lot of care is taken
+to ensure security and safety of this crate, including design (recursion limit, defensive
+programming), tests, and fuzzing. It also aims to be panic-free.
+
+The code is available on [Github](https://github.com/rusticata/x509-parser)
+and is part of the [Rusticata](https://github.com/rusticata) project.
+
+Certificates are usually encoded in two main formats: PEM (usually the most common format) or
+DER.  A PEM-encoded certificate is a container, storing a DER object. See the
+[`pem`](https://docs.rs/x509-parser/latest/x509_parser/pem/index.html) module for more documentation.
+
+To decode a DER-encoded certificate, the main parsing method is
+[`parse_x509_certificate`](https://docs.rs/x509-parser/latest/x509_parser/fn.parse_x509_certificate.html), which builds a
+[`X509Certificate`](https://docs.rs/x509-parser/latest/x509_parser/x509/struct.X509Certificate.html) object.
+
+The returned objects for parsers follow the definitions of the RFC. This means that accessing
+fields is done by accessing struct members recursively. Some helper functions are provided, for
+example [X509Certificate::issuer()](https://docs.rs/x509-parser/latest/x509_parser/x509/struct.X509Certificate.html#method.issuer) returns the
+same as accessing `<object>.tbs_certificate.issuer`.
+
+For PEM-encoded certificates, use the [`pem`](https://docs.rs/x509-parser/latest/x509_parser/pem/index.html) module.
+
+# Examples
+
+Parsing a certificate in DER format:
+
+```rust
+use x509_parser::prelude::*;
+
+static IGCA_DER: &[u8] = include_bytes!("../assets/IGC_A.der");
+
+let res = parse_x509_certificate(IGCA_DER);
+match res {
+    Ok((rem, cert)) => {
+        assert!(rem.is_empty());
+        //
+        assert_eq!(cert.tbs_certificate.version, X509Version::V3);
+    },
+    _ => panic!("x509 parsing failed: {:?}", res),
+}
+```
+
+To parse a CRL and print information about revoked certificates:
+
+```rust
+#
+#
+let res = parse_x509_crl(DER);
+match res {
+    Ok((_rem, crl)) => {
+        for revoked in crl.iter_revoked_certificates() {
+            println!("Revoked certificate serial: {}", revoked.raw_serial_as_string());
+            println!("  Reason: {}", revoked.reason_code().unwrap_or_default().1);
+        }
+    },
+    _ => panic!("CRL parsing failed: {:?}", res),
+}
+```
+
+See also `examples/print-cert.rs`.
+
+# Features
+
+- The `verify` feature adds support for (cryptographic) signature verification, based on `ring`.
+  It adds the
+  [X509Certificate::verify_signature()](https://docs.rs/x509-parser/latest/x509_parser/x509/struct.X509Certificate.html#method.verify_signature)
+  to `X509Certificate`.
+
+```rust
+/// Cryptographic signature verification: returns true if certificate was signed by issuer
+#[cfg(feature = "verify")]
+pub fn check_signature(cert: &X509Certificate<'_>, issuer: &X509Certificate<'_>) -> bool {
+    let issuer_public_key = &issuer.tbs_certificate.subject_pki;
+    cert
+        .verify_signature(Some(issuer_public_key))
+        .is_ok()
+}
+```
+
+## Rust version requirements
+
+`x509-parser` requires **Rustc version 1.45 or greater**, based on nom 6
+dependencies and for proc-macro attributes support.
+
+[RFC5280]: https://tools.ietf.org/html/rfc5280
+<!-- cargo-sync-readme end -->
+
+## Changes
+
+See [CHANGELOG.md](CHANGELOG.md)
+
+# 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.