Tidy a few markdown lints

See https://marketplace.visualstudio.com/items?itemName=DavidAnson.vscode-markdownlint
for the tool used to reveal markdown lint

Author: shaun-cox

CONTRIBUTING.md

@@ -29,7 +29,7 @@ add new tests.
 [code structure section]: #code-structure
 [testing section]: #testing
 
-# Code structure
+## Code structure
 
 All types and methods that are available on all tier 1 platforms are defined in
 the first level of the source, i.e. `src/*.rs` files. Additional API that is
@@ -55,7 +55,7 @@ Other types are mostly defined in `src/lib.rs`, except for `SockAddr` and
 `Socket`, where OS specific methods are defined in `src/sys/*.rs`, e.g.
 `Type::cloexec`.
 
-# Testing
+## Testing
 
 Testing Socket2 is as simple as running `cargo test --all-features`.
 
@@ -71,7 +71,7 @@ targets can be installed automatically using `make install_targets` (which uses
 [cargo-hack]: https://crates.io/crates/cargo-hack
 [rustup]: https://rustup.rs
 
-## Adding a test
+### Adding a test
 
 Tests should be added to `tests/socket.rs`, following (roughly) the same order
 in which the methods are defined on a type. At the bottom of this file it has a

README.md

@@ -19,21 +19,22 @@ See the [API documentation] for more.
 
 [API documentation]: https://docs.rs/socket2
 
-# Branches
+## Branches
 
 Currently Socket2 supports the following versions:
- * v0.6 developed in the master branch
- * v0.5 developed in the [v0.5.x branch]
- * v0.4 developed in the [v0.4.x branch]
+
+* v0.6 developed in the master branch
+* v0.5 developed in the [v0.5.x branch]
+* v0.4 developed in the [v0.4.x branch]
 
 [v0.5.x branch]: https://github.com/rust-lang/socket2/tree/v0.5.x
 [v0.4.x branch]: https://github.com/rust-lang/socket2/tree/v0.4.x
 
-# OS support
+## OS support
 
 Socket2 attempts to support the same OS/architectures as Rust does, see
-https://doc.rust-lang.org/nightly/rustc/platform-support.html. However this is
-not always possible, below is current list of support OSs.
+[platform support](https://doc.rust-lang.org/nightly/rustc/platform-support.html).
+However this is not always possible, below is current list of support OSs.
 
 *If your favorite OS is not on the list consider contributing it!*
 
@@ -63,18 +64,18 @@ feature flag.
 * Solaris
 * OpenHarmony
 
-# Minimum Supported Rust Version (MSRV)
+## Minimum Supported Rust Version (MSRV)
 
 Socket2 uses 1.70.0 as MSRV.
 
-# License
+## License
 
 This project is licensed under either of
 
- * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
-   https://www.apache.org/licenses/LICENSE-2.0)
- * MIT license ([LICENSE-MIT](LICENSE-MIT) or
-   https://opensource.org/licenses/MIT)
+* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
+   <https://www.apache.org/licenses/LICENSE-2.0>)
+* MIT license ([LICENSE-MIT](LICENSE-MIT) or
+   <https://opensource.org/licenses/MIT>)
 
 at your option.