Changed most vec! invocations to use square braces

Most of the Rust community agrees that the vec! macro is clearer when
called using square brackets [] instead of regular brackets (). Most of
these ocurrences are from before macros allowed using different types of
brackets.

There is one left unchanged in a pretty-print test, as the pretty
printer still wants it to have regular brackets.

src/librustdoc/html/render.rs

@@ -1260,7 +1260,7 @@ impl Context {
         item.name = Some(krate.name);
 
         // render the crate documentation
-        let mut work = vec!((self, item));
+        let mut work = vec![(self, item)];
 
         while let Some((mut cx, item)) = work.pop() {
             cx.item(item, |cx, item| {