Android Extensions: Add missing documentation, move the hasCache property to the compiler module

plugins/android-extensions/android-extensions-runtime/src/kotlinx/android/parcel/IgnoredOnParcel.kt

@@ -16,6 +16,9 @@
 
 package kotlinx.android.parcel
 
+/**
+ * The property annotated with [IgnoredOnParcel] will not be stored into parcel.
+ */
 @Target(AnnotationTarget.PROPERTY)
 @Retention(AnnotationRetention.SOURCE)
 annotation class IgnoredOnParcel

plugins/android-extensions/android-extensions-runtime/src/kotlinx/android/parcel/Parceler.kt

@@ -20,6 +20,9 @@ package kotlinx.android.parcel
 import android.os.Parcel
 import android.os.Parcelable
 
+/**
+ * The base interface for custom [Parcelize] serializers.
+ */
 interface Parceler<T> {
     /**
      * Writes the [T] instance state to the [parcel].