docs: lots of additions to the resources docs

new drawable resources
add <merge> and <include> to layout resource
update drawable class descriptioons to point to resources guide
add ID resource type

Change-Id: I733eec50bb2671f28c9e6dd7dec14eb6586f5193

graphics/java/android/graphics/drawable/AnimationDrawable.java

@@ -64,6 +64,8 @@ import android.util.AttributeSet;
  * // Start the animation (looped playback by default).
  * frameAnimation.start()
  * </pre>
+ * <p>For more information, see the guide to <a
+ * href="{@docRoot}guide/topics/resources/animation-resource.html">Animation Resources</a>.</p>
  *
  * @attr ref android.R.styleable#AnimationDrawable_visible
  * @attr ref android.R.styleable#AnimationDrawable_variablePadding