chore: Fix rustdoc lints

Author: jayvdb

src/lib.rs

@@ -1,3 +1,4 @@
+#![allow(rustdoc::invalid_html_tags)]
 //! # Async version of the Rust standard library
 //!
 //! `async-std` is a foundation of portable Rust software, a set of minimal and battle-tested
@@ -191,7 +192,7 @@
 //! <span
 //!   class="module-item stab portability"
 //!   style="display: inline; border-radius: 3px; padding: 2px; font-size: 80%; line-height: 1.2;"
-//! ><code>unstable</code></span>
+//! > <code>unstable</code> </span>
 //! are available only when the `unstable` Cargo feature is enabled:
 //!
 //! ```toml
@@ -204,7 +205,7 @@
 //! <span
 //!   class="module-item stab portability"
 //!   style="display: inline; border-radius: 3px; padding: 2px; font-size: 80%; line-height: 1.2;"
-//! ><code>attributes</code></span>
+//! > <code>attributes</code> </span>
 //! are available only when the `attributes` Cargo feature is enabled:
 //!
 //! ```toml

src/sync/mod.rs

@@ -95,9 +95,9 @@
 //!   at the same time: In multi-threaded scenarios, you can use two
 //!   kinds of primitives to deal with synchronization:
 //!   - [memory fences] to ensure memory accesses are made visible to
-//!   other CPUs in the right order.
+//!     other CPUs in the right order.
 //!   - [atomic operations] to ensure simultaneous access to the same
-//!   memory location doesn't lead to undefined behavior.
+//!     memory location doesn't lead to undefined behavior.
 //!
 //! [prefetching]: https://en.wikipedia.org/wiki/Cache_prefetching
 //! [compiler fences]: https://doc.rust-lang.org/std/sync/atomic/fn.compiler_fence.html

src/task/block_on.rs

@@ -19,11 +19,9 @@ use crate::task::Builder;
 /// ```no_run
 /// use async_std::task;
 ///
-/// fn main() {
-///     task::block_on(async {
-///         println!("Hello, world!");
-///     })
-/// }
+/// task::block_on(async {
+///     println!("Hello, world!");
+/// })
 /// ```
 #[cfg(not(target_os = "unknown"))]
 pub fn block_on<F, T>(future: F) -> T