exp/template/html: flesh out package documentation.

R=nigeltao, r
CC=golang-dev
https://golang.org/cl/4969078

src/pkg/exp/template/html/Makefile

@@ -9,6 +9,7 @@ GOFILES=\
 	clone.go\
 	context.go\
 	css.go\
+	doc.go\
 	escape.go\
 	html.go\
 	js.go\

src/pkg/exp/template/html/escape.go

@@ -2,9 +2,6 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Package html is a specialization of template that automates the
-// construction of safe HTML output.
-// INCOMPLETE.
 package html
 
 import (