Missing proguard rules

[dzolnai]

In StackLayoutManager.kt, the class construct an animation and a layout using a declared constructor. These constructors get stripped by ProGuard, and the app will display the following exception:

I added these rules to prevent the exception:

-keepclassmembers class * extends com.littlemango.stacklayoutmanager.StackAnimation {
  public protected <init>(...);
}
-keepclassmembers class * extends com.littlemango.stacklayoutmanager.StackLayout {
  public protected <init>(...);
}

Maybe they can be optimized furthermore, these seem to work fine for me.

It would be nice if the rules could be exposed via consumerProguardFiles so that including projects have these rules automatically added.