cmd/godoc: add support for doc.Package.Notes

Add support for displaying the notes of the form 'MARKER(userid): comment' now collected by the go/doc package. Any two or more uppercase letters are recognised as a marker.

R=gri, rsc, bradfitz
CC=golang-dev
https://golang.org/cl/7334044

lib/godoc/package.html

@@ -73,6 +73,11 @@
 			{{if .Bugs}}
 				<dd><a href="#pkg-bugs">Bugs</a></dd>
 			{{end}}
+			{{if .Notes}}
+                                {{range $marker, $item := .Notes}}
+				<dd><a href="#pkg-{{$marker}}">{{$marker}}</a></dd>
+                                {{end}}
+			{{end}}
 			</dl>
 			</div><!-- #manual-nav -->
 
@@ -168,6 +173,14 @@
 		{{comment_html .}}
 		{{end}}
 	{{end}}
+	{{with .Notes}}
+                {{range $marker, $content := .}}
+		    <h2 id="pkg-{{$marker}}">{{$marker}}</h2>
+		    {{range .}}
+		    {{comment_html .}}
+                    {{end}}
+		{{end}}
+	{{end}}
 {{end}}
 
 {{with .PAst}}

lib/godoc/package.txt

@@ -61,7 +61,12 @@ TYPES
 BUGS
 
 {{range .}}{{comment_text . "    " "\t"}}
-{{end}}{{end}}{{end}}{{/*
+{{end}}{{end}}{{with .Notes}}
+{{range $marker, $content := .}}
+{{$marker}}
+
+{{range $content}}{{comment_text . "    " "\t"}}
+{{end}}{{end}}{{end}}{{end}}{{/*
 
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