Add redirects on the unstable docs.

This adds some redirects so if there are any links to old documentation,
they will get redirect to new documentation.

Author: ehuss

src/doc/src/reference/unstable.md

@@ -1060,3 +1060,35 @@ name = "mypackage"
 version = "0.0.1"
 rust-version = "1.42"
 ```
+
+<script>
+(function() {
+    var fragments = {
+        "#edition": "manifest.html#the-edition-field",
+        "#compile-progress": "config.html#termprogresswhen",
+        "#rename-dependency": "specifying-dependencies.html#renaming-dependencies-in-cargotoml",
+        "#alternate-registries": "registries.html",
+        "#offline-mode": "../commands/cargo.html",
+        "#publish-lockfile": "../commands/cargo-package.html",
+        "#default-run": "manifest.html#the-default-run-field",
+        "#cache-messages": "https://github.com/rust-lang/cargo/pull/7450",
+        "#install-upgrade": "../commands/cargo-install.html",
+        "#profile-overrides": "profiles.html#overrides",
+        "#config-profiles": "config.html#profile",
+        "#crate-versions": "https://github.com/rust-lang/cargo/pull/8509",
+        "#features": "features.html#feature-resolver-version-2",
+        "#package-features": "features.html#resolver-version-2-command-line-flags",
+        "#resolver": "resolver.html#resolver-versions",
+    };
+    var target = fragments[window.location.hash];
+    if (target) {
+        if (target.startsWith('https')) {
+          window.location.replace(target);
+        } else {
+          var url = window.location.toString();
+          var base = url.substring(0, url.lastIndexOf('/'));
+          window.location.replace(base + "/" + target);
+        }
+    }
+})();
+</script>