Update the overview to include details about library projects.

docs/src/main/sphinx/overview.rst

@@ -10,18 +10,50 @@ this documentation.
 ROS-enabling Android applications
 ----------------------------------
 
-android_core provides a base `Activity`_
-(:javadoc:`org.ros.android.RosActivity`) and `Service`_
-(:javadoc:`org.ros.android.NodeMainExecutorService`) for executing
+android_core provides `Android Library Projects`_ to help you write ROS
+applications for Android. The library projects are named for the `Android API
+level`_ they require (e.g. android_gingerbread and android_honeycomb_mr2).
+Each class or feature is defined in the library project that represents the
+minimum version of Android required for it to work.
+
+Your application can depend on multiple library projects. This allows you to
+easily target your application for different API levels.
+
+Beyond specific features, android_core defines the pattern of combining the
+Android `View`_ and :javadoc:`org.ros.node.NodeMain` concepts to enable the
+development of data driven Android UIs (e.g.
+:javadoc:`org.ros.android.view.RosTextView`).
+
+.. _Android Library Projects: http://developer.android.com/guide/developing/projects/index.html#LibraryProjects
+.. _Android API level: http://developer.android.com/guide/appendix/api-levels.html
+.. _View: http://developer.android.com/reference/android/view/View.html
+
+android_gingerbread library project
+-----------------------------------
+
+android_gingerbread (API level 9) is the lowest API level supported. It
+provides the base `Activity`_ (:javadoc:`org.ros.android.RosActivity`) and
+`Service`_ (:javadoc:`org.ros.android.NodeMainExecutorService`) for executing
 and managing the lifecycle of your :javadoc:`org.ros.node.NodeMain`\s.
 
-In addition, android_core defines the pattern of combining the Android
-`View`_ and :javadoc:`org.ros.node.NodeMain` concepts to enable the
-development of data driven Android UIs. Several such RosViews (e.g.
-:javadoc:`org.ros.android.view.RosTextView`,
-:javadoc:`org.ros.android.view.RosImageView`, and
-:javadoc:`org.ros.android.view.RosCameraPreviewView`) are provided.
+A few of the other features provided include:
+
+* camera publisher
+* image view
+* orientation publisher
 
 .. _Activity: http://developer.android.com/reference/android/app/Activity.html
 .. _Service: http://developer.android.com/reference/android/app/Service.html
-.. _View: http://developer.android.com/reference/android/view/View.html
+
+android_honeycomb_mr2 library project
+-------------------------------------
+
+android_honeycomb_mr2 (API level 13) provides features that require multitouch
+and other APIs that are only available in devices with Android Honeycomb MR2 or
+higher.
+
+A few of the features provided include:
+
+* 2D mapping and navigation
+* 2D laser scan visualization
+* virtual joystick