Added a fuzzer as integration to OSS-Fuzz. (chronotope#463)

* Added a fuzzer.

* Added a README for the fuzzer set up.

fuzz/.gitignore

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+
+target
+corpus
+artifacts

fuzz/Cargo.toml

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+
+[package]
+name = "chrono-fuzz"
+version = "0.0.0"
+authors = ["David Korczynski <[email protected]>"]
+publish = false
+edition = "2018"
+
+[package.metadata]
+cargo-fuzz = true
+
+[dependencies]
+libfuzzer-sys = "0.3"
+
+[dependencies.chrono]
+path = ".."
+
+# Prevent this from interfering with workspaces
+[workspace]
+members = ["."]
+
+[[bin]]
+name = "fuzz_reader"
+path = "fuzz_targets/fuzz_reader.rs"

fuzz/README.md

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+# Fuzzing Chrono
+To fuzz Chrono we rely on the [Cargo-fuzz](https://rust-fuzz.github.io/) project. 
+
+To install cargo-fuzz:
+```
+cargo install cargo-fuzz
+```
+
+To run the Chrono fuzzer, navigate to the top directory of chrono and issue the following command:
+```
+cargo-fuzz run fuzz_reader
+```

fuzz/fuzz_targets/fuzz_reader.rs

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+#![no_main]
+use libfuzzer_sys::fuzz_target;
+
+fuzz_target!(|data: &[u8]| {
+    use chrono::prelude::*;
+    if let Ok(data) = std::str::from_utf8(data) {
+        let _ = DateTime::parse_from_rfc2822(data);
+        let _ = DateTime::parse_from_rfc3339(data);
+    }
+});