Added library-level comments for polymer and polymer_expressions

pkg/polymer_expressions/README.md

Index: pkg/polymer_expressions/README.md
diff --git a/pkg/polymer_expressions/README.md b/pkg/polymer_expressions/README.md
index 5a7e9b29cbd40e4c163ca5027f93096466c01996..c71f71e16b213474e93eac3082b29d0fe6a9ba82 100644
--- a/pkg/polymer_expressions/README.md
+++ b/pkg/polymer_expressions/README.md
@@ -1,8 +1,25 @@
 polymer_expressions
 ===================
 
-Polymer Expressions are an expressive syntax that can be used in templates in
-Dart. Polymer Expressions allow you to write complex binding expressions, with
+
+Polymer expressions are an expressive syntax that can be used in HTML templates
+with Dart.
+
+Templates are one feature of Polymer.dart -- a set of comprehensive UI

[Kathy Walrath, 2013/09/13 16:44:16]

Can you use the character '—' (shift-option-dash on a Mac)?

[mem, 2013/09/13 17:05:58]

It just looks like a regular dash. I even tried to copy the one you used.
Is comma better?

mem

On 2013/09/13 16:44:16, Kathy Walrath wrote:

[Kathy Walrath, 2013/09/13 19:59:55]

I think it looks like a regular dash in vim or reviews because they use a
fixed-width font. It seems to look right in the generated docs.

On 2013/09/13 17:05:58, mem wrote:

+and utility components for building web applications.
+This package is automatically included with the
+[Polymer](https://pub.dartlang.org/packages/polymer) package
+because Polymer expressions are the default expression syntax
+in Polymer Dart apps.
+The [Polymer.dart home page][home_page]

[Kathy Walrath, 2013/09/13 16:44:16]

I believe Google style is to say "homepage".

In fact, when I use Google to search for "homepage" or "home page", I get an ad:
"Make Google Your Homepage"!

[mem, 2013/09/13 17:05:58]

Done.

+contains a list of features, project status,
+installation instructions, tips for upgrading from Web UI,

[Kathy Walrath, 2013/09/13 16:44:16]

hey, you worded the Web UI thing better here

[mem, 2013/09/13 17:05:58]

:-)

Just testing your editing skills!
mem

On 2013/09/13 16:44:16, Kathy Walrath wrote:

+and links to other documentation.
+
+
+## Overview
+
+Polymer expressions allow you to write complex binding expressions, with
 property access, function invocation, list/map indexing, and two-way filtering
 like:
 
@@ -10,8 +27,6 @@ like:
     {{ person.title + " " + person.getFullName() | upppercase }}
 ```
 
-## Overview
-
 ### Model-Driven Views (MDV)
 [MDV][mdv] allows you to define templates directly in HTML that are rendered by the
 browser into the DOM. Templates are bound to a data model, and changes to the