[release-branch.go1.12] doc/go1.12: document net/url.Parse now rejecting ASCII CTLs

Updates #27302
Updates #22907

Change-Id: Iac6957f3517265dfb9c662efb7af31192e3bfd6c
Reviewed-on: https://go-review.googlesource.com/c/162960Reviewed-by: Ian Lance Taylor <iant@golang.org>
(cherry picked from commit ef454fd5)
Reviewed-on: https://go-review.googlesource.com/c/162826

doc/go1.12.html

@@ -694,6 +694,20 @@ for {
 
 </dl><!-- net/http -->
 
+<dl id="net/url"><dt><a href="/pkg/net/url/">net/url</a></dt>
+  <dd>
+    <p><!-- CL 159157, CL 160178 -->
+      <a href="/pkg/net/url/#Parse"><code>Parse</code></a>,
+      <a href="/pkg/net/url/#ParseRequestURI"><code>ParseRequestURI</code></a>,
+      and
+      <a href="/pkg/net/url/#URL.Parse"><code>URL.Parse</code></a>
+      now return an
+      error for URLs containing ASCII control characters, which includes NULL,
+      tab, and newlines.
+    </p>
+
+</dl><!-- net/url -->
+
 <dl id="net/http/httputil"><dt><a href="/pkg/net/http/httputil/">net/http/httputil</a></dt>
   <dd>
     <p><!-- CL 146437 -->