Update for format of Android audio, from .amr to .aac.
This closes #124
### Android Quirks
-- Android devices record audio in Adaptive Multi-Rate format. The specified file should end with a _.amr_ extension.
+- Android devices record audio in AAC ADTS file format. The specified file should end with a _.aac_ extension.
- The hardware volume controls are wired up to the media volume while any Media objects are alive. Once the last created Media object has `release()` called on it, the volume controls revert to their default behaviour. The controls are also reset on page navigation, as this releases all Media objects.
### iOS Quirks