Add appengine/gcloud/mustache dependencies.

pkg/appengine/CHANGELOG.md

+## 0.2.4
+
+* Added withAppEngineServices() function which allows running arbitrary code
+  using AppEngine services via a service scope.
+
+## 0.2.4
+
+* Run request handlers inside a service scope
+(see `package:gcloud/service_scope.dart`).
+* Insert an authenticated HTTP client into the service scope.
+* Insert a `memcacheService` into the service scope.
+* Added `isDevelopmentServer` and `isProductionEnvironment` getter to client
+context.
+* Make hostnames returned from modules service use -dot- naming to support
+HTTPS.
+* Mark `package:appengine/remote_api.dart` as deprecated.
+
+## 0.2.3
+
+* Small bugfix in the lowlevel memcache API implementation.
+
+## 0.2.2
+
+* Updated `README.md`
+* Widen googleapis_auth constraint to include version 0.2.0
+
+## 0.2.1
+
+* Small bugfix in storage API implementation
+* respect DART_PUB_SERVE url only in developer mode
+* sync db/datastore tests to the ones used in gcloud
+
+## 0.2.0
+
+* Use datastore/db APIs from package:gcloud
+    * simplified annotation system
+    * paging-based query API
+* Added module service
+* Some bugfixes
+
+## 0.1.0
+
+* Alpha release