Rollup merge of #44072 - lukaramu:fix-doc-headings, r=steveklabnik

Fix inconsistent doc headings

This fixes headings reading "Unsafety" and "Example", they should be "Safety" and "Examples" according to RFC 1574.

r? @steveklabnik

src/libstd/io/mod.rs

@@ -522,7 +522,7 @@ pub trait Read {
     /// `Read`er - the method only takes `&self` so that it can be used through
     /// trait objects.
     ///
-    /// # Unsafety
+    /// # Safety
     ///
     /// This method is unsafe because a `Read`er could otherwise return a
     /// non-zeroing `Initializer` from another `Read` type without an `unsafe`
@@ -903,7 +903,7 @@ impl Initializer {
 
     /// Returns a new `Initializer` which will not zero out buffers.
     ///
-    /// # Unsafety
+    /// # Safety
     ///
     /// This may only be called by `Read`ers which guarantee that they will not
     /// read from buffers passed to `Read` methods, and that the return value of

src/libstd/memchr.rs

@@ -20,7 +20,7 @@
 /// magnitude faster than `haystack.iter().position(|&b| b == needle)`.
 /// (See benchmarks.)
 ///
-/// # Example
+/// # Examples
 ///
 /// This shows how to find the first position of a byte in a byte string.
 ///
@@ -40,7 +40,7 @@ pub fn memchr(needle: u8, haystack: &[u8]) -> Option<usize> {
 /// Returns the index corresponding to the last occurrence of `needle` in
 /// `haystack`, or `None` if one is not found.
 ///
-/// # Example
+/// # Examples
 ///
 /// This shows how to find the last position of a byte in a byte string.
 ///

src/libstd/sys/redox/ext/mod.rs

@@ -13,7 +13,7 @@
 //! For now, this module is limited to extracting file descriptors,
 //! but its functionality will grow over time.
 //!
-//! # Example
+//! # Examples
 //!
 //! ```no_run
 //! use std::fs::File;

src/libstd/sys/unix/ext/mod.rs

@@ -13,7 +13,7 @@
 //! For now, this module is limited to extracting file descriptors,
 //! but its functionality will grow over time.
 //!
-//! # Example
+//! # Examples
 //!
 //! ```no_run
 //! use std::fs::File;

src/libstd/thread/mod.rs

@@ -807,7 +807,7 @@ pub fn park_timeout_ms(ms: u32) {
 /// Platforms which do not support nanosecond precision for sleeping will have
 /// `dur` rounded up to the nearest granularity of time they can sleep for.
 ///
-/// # Example
+/// # Examples
 ///
 /// Waiting for the complete expiration of the timeout:
 ///