Replace VecDeque with stream::from_iter in examples (#447)

src/option/sum.rs

@@ -20,12 +20,10 @@ where
         ```
         # fn main() { async_std::task::block_on(async {
         #
-        use std::collections::VecDeque;
         use async_std::prelude::*;
+        use async_std::stream;
 
-        let words: VecDeque<_> = vec!["have", "a", "great", "day"]
-            .into_iter()
-            .collect();
+        let words = stream::from_iter(vec!["have", "a", "great", "day"]);
         let total: Option<usize> = words.map(|w| w.find('a')).sum().await;
         assert_eq!(total, Some(5));
         #

src/result/product.rs

@@ -20,10 +20,10 @@ where
         ```
         # fn main() { async_std::task::block_on(async {
         #
-        use std::collections::VecDeque;
         use async_std::prelude::*;
+        use async_std::stream;
 
-        let v: VecDeque<_> = vec![1, 2, 4].into_iter().collect();
+        let v = stream::from_iter(vec![1, 2, 4]);
         let res: Result<i32, &'static str> = v.map(|x|
             if x < 0 {
                 Err("Negative element found")

src/result/sum.rs

@@ -20,10 +20,10 @@ where
         ```
         # fn main() { async_std::task::block_on(async {
         #
-        use std::collections::VecDeque;
         use async_std::prelude::*;
+        use async_std::stream;
 
-        let v: VecDeque<_> = vec![1, 2].into_iter().collect();
+        let v = stream::from_iter(vec![1, 2]);
         let res: Result<i32, &'static str> = v.map(|x|
             if x < 0 {
                 Err("Negative element found")

src/stream/from_iter.rs

@@ -12,7 +12,7 @@ pin_project! {
     /// See it documentation for more.
     ///
     /// [`from_iter`]: fn.from_iter.html
-    #[derive(Debug)]
+    #[derive(Clone, Debug)]
     pub struct FromIter<I> {
         iter: I,
     }