godoc: generate package toc in template, not in JavaScript

1. Generate TOC for package pages using template,
instead of using JavaScript magic.  This makes the
pages generated by godoc -html easier to export
to other systems.

2. Make TOC one column.  It's hard to do two columns
portably without invoking JavaScript.

3. Since the TOC is only one column, show full type
signatures for functions and methods.  Many times
that's all you need to see anyway.

4. Name the section after the TOC "Overview".
Naming it something is important, to set it off
from the TOC and so that there's a quick link to
it in the TOC.

For now, some illustrative examples:

http://swtch.com:6060/pkg/io/
http://swtch.com:6060/pkg/strings/
http://swtch.com:6060/pkg/tabwriter/
http://swtch.com:6060/pkg/unicode/

Fixes #1982.

R=gri, bradfitz, r
CC=golang-dev
https://golang.org/cl/5303044

doc/godocs.js

@@ -57,6 +57,7 @@ function godocs_bindSearchEvents() {
  * links.  "Decorates" the element with id=="nav" with this table of contents.
  */
 function godocs_generateTOC() {
+  if (document.getElementById('manual-nav')) { return; }
   var navbar = document.getElementById('nav');
   if (!navbar) { return; }
 

lib/godoc/package.html

@@ -3,10 +3,47 @@
 	Use of this source code is governed by a BSD-style
 	license that can be found in the LICENSE file.
 -->
+<!-- Table of contents; must be named manual-nav to turn off auto nav. -->
+<div id="manual-nav">
+{{with .PDoc}}
+	<dl>
+	<dd><a href="#Overview">Overview</a></dd>
+	{{if .Consts}}
+		<dd><a href="#Constants">Constants</a></dd>
+	{{end}}
+	{{if .Vars}}
+		<dd><a href="#Variables">Variables</a></dd>
+	{{end}}
+	{{range .Funcs}}
+		{{$name_html := html .Name}}
+		<dd><a href="#{{$name_html}}">{{node_html .Decl $.FSet}}</a></dd>
+	{{end}}
+	{{range .Types}}
+		{{$tname := printf "%s" .Type.Name}}
+		{{$tname_html := node_html .Type.Name $.FSet}}
+		<dd><a href="#{{$tname_html}}">type {{$tname_html}}</a></dd>
+		{{range .Factories}}
+			{{$name_html := html .Name}}
+			<dd>&nbsp; &nbsp; <a href="#{{$name_html}}">{{node_html .Decl $.FSet}}</a></dd>
+		{{end}}
+		{{range .Methods}}
+			{{$name_html := html .Name}}
+			<dd>&nbsp; &nbsp; <a href="#{{$tname_html}}.{{$name_html}}">{{node_html .Decl $.FSet}}</a></dd>
+		{{end}}
+	{{end}}
+	{{if .Bugs}}
+		<dd><a href="#Bugs">Bugs</a></dd>
+	{{end}}
+	</dl>
+{{end}}
+</div>
+
+<!-- Main page -->		
 {{with .PAst}}
 	<pre>{{node_html . $.FSet}}</pre>
 {{end}}
 {{with .PDoc}}
+	<h2 id="Overview">Overview</h2>
 	<!-- PackageName is printed as title by the top-level template -->
 	{{if $.IsPkg}}
 		<p><code>import "{{html .ImportPath}}"</code></p>
@@ -38,8 +75,7 @@
 			<pre>{{node_html .Decl $.FSet}}</pre>
 		{{end}}
 	{{end}}
-	{{with .Funcs}}
+	{{range .Funcs}}
-		{{range .}}
 		{{/* Name is a string - no need for FSet */}}
 		{{$name_html := html .Name}}
 		<h2 id="{{$name_html}}">func <a href="/{{posLink_url .Decl $.FSet}}">{{$name_html}}</a></h2>
@@ -47,9 +83,7 @@
 		{{comment_html .Doc}}
 		{{example_html .Name $.Examples $.FSet}}
 	{{end}}
-	{{end}}
+	{{range .Types}}
-	{{with .Types}}
-		{{range .}}
 		{{$tname := printf "%s" .Type.Name}}
 		{{$tname_html := node_html .Type.Name $.FSet}}
 		<h2 id="{{$tname_html}}">type <a href="/{{posLink_url .Decl $.FSet}}">{{$tname_html}}</a></h2>
@@ -80,7 +114,6 @@
 			{{example_html $name $.Examples $.FSet}}
 		{{end}}
 	{{end}}
-	{{end}}
 	{{with .Bugs}}
 		<h2 id="Bugs">Bugs</h2>
 		{{range .}}