Rollup merge of #40689 - GuillaumeGomez:rustdoc-associated-type-formatting, r=frewsxcv

Add whitespace around "=" in assoc items

Part of #40641.

r? @rust-lang/docs

Before:

<img width="1440" alt="screen shot 2017-03-20 at 22 42 34" src="https://cloud.githubusercontent.com/assets/3050060/24123102/89181d8c-0dbe-11e7-897c-841497cf7001.png">

After:

<img width="1440" alt="screen shot 2017-03-20 at 22 42 36" src="https://cloud.githubusercontent.com/assets/3050060/24123118/8dec176e-0dbe-11e7-9759-cabbd062a4c2.png">

src/test/rustdoc/doc-assoc-item.rs

@@ -0,0 +1,28 @@
+// Copyright 2017 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+pub struct Foo<T> {
+    x: T,
+}
+
+pub trait Bar {
+    type Fuu;
+
+    fn foo(foo: Self::Fuu);
+}
+
+// @has doc_assoc_item/struct.Foo.html '//*[@class="impl"]' 'impl<T: Bar<Fuu = u32>> Foo<T>'
+impl<T: Bar<Fuu = u32>> Foo<T> {
+    pub fn new(t: T) -> Foo<T> {
+        Foo {
+            x: t,
+        }
+    }
+}