Prepare for 0.28.0. (#1902)

* Update CHANGELOG and version number for 0.28.0

* Add appveyor status to README
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2eeafdd..c3984de 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,24 @@
+## 0.28.0
+* Fix a crash when a Dart library doesn't have the .dart suffix (#1897)
+* Fix a crash when a Dart file is loaded with an unresolvable
+  prefix import in analyzer (#1896)
+* Do not execute tools to generate documentation for non-canonical
+  elements that have canonical counterparts.  This eliminates
+  "duplicate" tool runs that serve no purpose for generated docs
+  or macro loading.  (#1898)
+* Fix a minor problem where invalid command line parameters could
+  generate an ugly exception (#1895)
+* Remove internal copy of mustache4dart and depend on the mustache
+  package.  Many minor changes to templating as a result.  (#1894)
+* **Breaking change to warning handling**.  Many new command line options
+  and dartdoc_options.yaml settings can constrain and configure
+  how warnings are interpreted by dartdoc, and whether they are fatal.
+  The old --show-warnings flag has been removed. (#1891, #1343, #1412, #1480)
+* Fix a crash when loading README.md files that have invalid UTF-8.
+  (#1890, #1889)
+* Early implementation of experiment flags for Dart tools, based
+  on the analyzer (#1884)
+
 ## 0.27.0
 * Several dartdoc project infrastructure changes, including coverage
   support. (#1869, #1878, #1879, #1881, #1882)
diff --git a/README.md b/README.md
index 748852d..5880cb5 100644
--- a/README.md
+++ b/README.md
@@ -1,6 +1,7 @@
 # dartdoc
 
 [![Build Status](https://travis-ci.org/dart-lang/dartdoc.svg?branch=master)](https://travis-ci.org/dart-lang/dartdoc)
+[![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/s6sh69et2ga00dlu?svg=true)](https://ci.appveyor.com/project/devoncarew/dartdoc)
 [![Coverage Status](https://coveralls.io/repos/github/dart-lang/dartdoc/badge.svg?branch=master)](https://coveralls.io/github/dart-lang/dartdoc?branch=master)
 
 
diff --git a/lib/src/version.dart b/lib/src/version.dart
index 20a0174..9aedebc 100644
--- a/lib/src/version.dart
+++ b/lib/src/version.dart
@@ -1,2 +1,2 @@
 // Generated code. Do not modify.
-const packageVersion = '0.27.0';
+const packageVersion = '0.28.0';
diff --git a/pubspec.yaml b/pubspec.yaml
index 8ee23cb..7d8e14b 100644
--- a/pubspec.yaml
+++ b/pubspec.yaml
@@ -1,6 +1,6 @@
 name: dartdoc
 # Also update the `version` field in lib/dartdoc.dart.
-version: 0.27.0
+version: 0.28.0
 author: Dart Team <misc@dartlang.org>
 description: A documentation generator for Dart.
 homepage: https://github.com/dart-lang/dartdoc