Move Poll::new method into a single impl block

Make the documentation a bit nicer. Usually the creation methods, such
as new, are the first methods in the first impl block, so that is where
people look for them.

src/poll.rs

@@ -234,6 +234,47 @@ pub struct Registry {
 }
 
 impl Poll {
+    cfg_os_poll! {
+        /// Return a new `Poll` handle.
+        ///
+        /// This function will make a syscall to the operating system to create
+        /// the system selector. If this syscall fails, `Poll::new` will return
+        /// with the error.
+        ///
+        /// See [struct] level docs for more details.
+        ///
+        /// [struct]: struct.Poll.html
+        ///
+        /// # Examples
+        ///
+        /// ```
+        /// # use std::error::Error;
+        /// # fn main() -> Result<(), Box<dyn Error>> {
+        /// use mio::{Poll, Events};
+        /// use std::time::Duration;
+        ///
+        /// let mut poll = match Poll::new() {
+        ///     Ok(poll) => poll,
+        ///     Err(e) => panic!("failed to create Poll instance; err={:?}", e),
+        /// };
+        ///
+        /// // Create a structure to receive polled events
+        /// let mut events = Events::with_capacity(1024);
+        ///
+        /// // Wait for events, but none will be received because no
+        /// // `event::Source`s have been registered with this `Poll` instance.
+        /// poll.poll(&mut events, Some(Duration::from_millis(500)))?;
+        /// assert!(events.is_empty());
+        /// #     Ok(())
+        /// # }
+        /// ```
+        pub fn new() -> io::Result<Poll> {
+            sys::Selector::new().map(|selector| Poll {
+                registry: Registry { selector },
+            })
+        }
+    }
+
     /// Create a separate `Registry` which can be used to register
     /// `event::Source`s.
     pub fn registry(&self) -> &Registry {
@@ -338,49 +379,6 @@ impl Poll {
     }
 }
 
-cfg_os_poll! {
-    impl Poll {
-        /// Return a new `Poll` handle.
-        ///
-        /// This function will make a syscall to the operating system to create
-        /// the system selector. If this syscall fails, `Poll::new` will return
-        /// with the error.
-        ///
-        /// See [struct] level docs for more details.
-        ///
-        /// [struct]: struct.Poll.html
-        ///
-        /// # Examples
-        ///
-        /// ```
-        /// # use std::error::Error;
-        /// # fn main() -> Result<(), Box<dyn Error>> {
-        /// use mio::{Poll, Events};
-        /// use std::time::Duration;
-        ///
-        /// let mut poll = match Poll::new() {
-        ///     Ok(poll) => poll,
-        ///     Err(e) => panic!("failed to create Poll instance; err={:?}", e),
-        /// };
-        ///
-        /// // Create a structure to receive polled events
-        /// let mut events = Events::with_capacity(1024);
-        ///
-        /// // Wait for events, but none will be received because no
-        /// // `event::Source`s have been registered with this `Poll` instance.
-        /// poll.poll(&mut events, Some(Duration::from_millis(500)))?;
-        /// assert!(events.is_empty());
-        /// #     Ok(())
-        /// # }
-        /// ```
-        pub fn new() -> io::Result<Poll> {
-            sys::Selector::new().map(|selector| Poll {
-                registry: Registry { selector },
-            })
-        }
-    }
-}
-
 #[cfg(unix)]
 impl AsRawFd for Poll {
     fn as_raw_fd(&self) -> RawFd {