Update to Rust edition 2021

Bump the edition (only 3 years late...) and do some other miscellaneous cleanup.

.editorconfig

@@ -0,0 +1,9 @@
+[*]
+indent_style = space
+indent_size = 4
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+
+[*.{yaml,yml}]
+indent_size = 2

.github/workflows/ci.yml

@@ -11,12 +11,6 @@ jobs:
           - windows-latest
     runs-on: ${{ matrix.os }}
     steps:
-      - uses: actions/checkout@v2
-
-      - uses: actions-rs/toolchain@v1
-        with:
-          profile: minimal
-          toolchain: stable
-          default: true
+      - uses: actions/checkout@v4
 
       - run: cargo test --workspace

CODEOWNERS

@@ -0,0 +1 @@
+* [email protected]

Cargo.toml

@@ -7,7 +7,7 @@ license = "MIT"
 repository = "https://github.com/sagebind/stability"
 documentation = "https://docs.rs/stability/"
 readme = "README.md"
-edition = "2018"
+edition = "2021"
 
 [dependencies]
 quote = "1"

example/Cargo.toml

@@ -3,7 +3,7 @@ name = "stability-example"
 version = "0.0.0"
 description = "Example crate demonstrating stablity usage."
 authors = ["Stephen M. Coakley <[email protected]>"]
-edition = "2018"
+edition = "2021"
 publish = false
 
 [features]

src/unstable.rs

@@ -42,14 +42,14 @@ impl UnstableAttribute {
             if let Some(issue) = &self.issue {
                 let doc_addendum = format!(
                     "\n\
-					# Availability\n\
-					\n\
-					**This API is marked as unstable** and is only available when \
-					the `{}` crate feature is enabled. This comes with no stability \
-					guarantees, and could be changed or removed at any time.
+                    # Availability\n\
+                    \n\
+                    **This API is marked as unstable** and is only available when \
+                    the `{}` crate feature is enabled. This comes with no stability \
+                    guarantees, and could be changed or removed at any time.
 
 The tracking issue is: `{}`
-				",
+                ",
                     feature_name, issue
                 );
                 item.push_attr(parse_quote! {
@@ -58,12 +58,12 @@ The tracking issue is: `{}`
             } else {
                 let doc_addendum = format!(
                     "\n\
-					# Availability\n\
-					\n\
-					**This API is marked as unstable** and is only available when \
-					the `{}` crate feature is enabled. This comes with no stability \
-					guarantees, and could be changed or removed at any time.\
-				",
+                    # Availability\n\
+                    \n\
+                    **This API is marked as unstable** and is only available when \
+                    the `{}` crate feature is enabled. This comes with no stability \
+                    guarantees, and could be changed or removed at any time.\
+                ",
                     feature_name
                 );
                 item.push_attr(parse_quote! {