Auto merge of #7983 - ehuss:fix-old-manifest-anchors, r=alexcrichton

Support old html anchors in manifest chapter.

#7733 unintentionally broke some old HTML anchors in the manifest chapter.  This would cause any links out in the wild to not scroll to the correct position.

Unfortunately it is too late for the 1.42 release.  However, I'd like to backport this for 1.43.

Author: bors

src/doc/src/reference/manifest.md

@@ -95,6 +95,7 @@ Versioning](https://semver.org/), so make sure you follow some basic rules:
   traits, fields, types, functions, methods or anything else.
 * Use version numbers with three numeric parts such as 1.0.0 rather than 1.0.
 
+<a id="the-authors-field-optional"></a>
 #### The `authors` field
 
 The `authors` field lists people or organizations that are considered the
@@ -106,6 +107,7 @@ brackets at the end of each author.
 
 > **Note**: [crates.io] requires at least one author to be listed.
 
+<a id="the-edition-field-optional"></a>
 #### The `edition` field
 
 You can opt in to a specific [Rust Edition] for your package with the
@@ -137,6 +139,7 @@ description = "A short description of my package"
 
 > **Note**: [crates.io] requires the `description` to be set.
 
+<a id="the-documentation-field-optional"></a>
 #### The `documentation` field
 
 The `documentation` field specifies a URL to a website hosting the crate's
@@ -259,6 +262,7 @@ categories = ["command-line-utilities", "development-tools::cargo-plugins"]
 > match one of the strings available at <https://crates.io/category_slugs>, and
 > must match exactly.
 
+<a id="the-workspace--field-optional"></a>
 #### The `workspace` field
 
 The `workspace` field can be used to configure the workspace that this package
@@ -280,6 +284,7 @@ table defined. That is, a crate cannot both be a root crate in a workspace
 For more information, see the [workspaces chapter](workspaces.md).
 
 <a id="package-build"></a>
+<a id="the-build-field-optional"></a>
 #### The `build` field
 
 The `build` field specifies a file in the package root which is a [build
@@ -299,6 +304,7 @@ The default is `"build.rs"`, which loads the script from a file named
 specify a path to a different file or `build = false` to disable automatic
 detection of the build script.
 
+<a id="the-links-field-optional"></a>
 #### The `links` field
 
 The `links` field specifies the name of a native library that is being linked
@@ -313,6 +319,7 @@ script guide.
 links = "foo"
 ```
 
+<a id="the-exclude-and-include-fields-optional"></a>
 #### The `exclude` and `include` fields
 
 You can explicitly specify that a set of file patterns should be ignored or
@@ -375,6 +382,7 @@ if any of those files change.
 
 [gitignore]: https://git-scm.com/docs/gitignore
 
+<a id="the-publish--field-optional"></a>
 #### The `publish` field
 
 The `publish` field can be used to prevent a package from being published to a
@@ -396,6 +404,7 @@ allowed to be published to.
 publish = ["some-registry-name"]
 ```
 
+<a id="the-metadata-table-optional"></a>
 #### The `metadata` table
 
 Cargo by default will warn about unused keys in `Cargo.toml` to assist in
@@ -539,7 +548,7 @@ more detail.
         "#integration-tests": "cargo-targets.html#integration-tests",
         "#configuring-a-target": "cargo-targets.html#configuring-a-target",
         "#target-auto-discovery": "cargo-targets.html#target-auto-discovery",
-        "#the-required-features-field": "cargo-targets.html#the-required-features-field",
+        "#the-required-features-field-optional": "cargo-targets.html#the-required-features-field",
         "#building-dynamic-or-static-libraries": "cargo-targets.html#the-crate-type-field",
         "#the-workspace-section": "workspaces.html#the-workspace-section",
         "#virtual-manifest": "workspaces.html",