Change the way that events are represented.

The bulk of this commit is changing instances of Vec to RingBuf which is
optimized for the push_back() / pop_front() strategy that is used
internaly in the event system.

The glutin custom iterators are now just wrappers around the RingBuf
iterator type.  This will bring the running time of iterator traversal from
O(n^2) to O(n) because shifting-on-delete won't be performed.

src/win32/mod.rs

@@ -1,5 +1,6 @@
 use std::sync::atomic::AtomicBool;
 use std::ptr;
+use std::collections::RingBuf;
 use libc;
 use {CreationError, Event};
 
@@ -14,7 +15,7 @@ mod gl;
 mod init;
 mod monitor;
 
-/// 
+///
 pub struct HeadlessContext(Window);
 
 impl HeadlessContext {
@@ -105,7 +106,7 @@ impl Window {
     }
 
     /// See the docs in the crate root file.
-    /// 
+    ///
     /// Calls SetWindowText on the HWND.
     pub fn set_title(&self, text: &str) {
         unsafe {
@@ -200,11 +201,11 @@ impl Window {
 
     /// See the docs in the crate root file.
     // TODO: return iterator
-    pub fn poll_events(&self) -> Vec<Event> {
-        let mut events = Vec::new();
+    pub fn poll_events(&self) -> RingBuf<Event> {
+        let mut events = RingBuf::new();
         loop {
             match self.events_receiver.try_recv() {
-                Ok(ev) => events.push(ev),
+                Ok(ev) => events.push_back(ev),
                 Err(_) => break
             }
         }
@@ -214,13 +215,13 @@ impl Window {
             use std::sync::atomic::Relaxed;
             self.is_closed.store(true, Relaxed);
         }
-        
+
         events
     }
 
     /// See the docs in the crate root file.
     // TODO: return iterator
-    pub fn wait_events(&self) -> Vec<Event> {
+    pub fn wait_events(&self) -> RingBuf<Event> {
         match self.events_receiver.recv_opt() {
             Ok(ev) => {
                 // if the received event is `Closed`, setting `is_closed` to true
@@ -241,7 +242,7 @@ impl Window {
             Err(_) => {
                 use std::sync::atomic::Relaxed;
                 self.is_closed.store(true, Relaxed);
-                vec![]
+                RingBuf::new()
             }
         }
     }