Merge: Android assets, resources, and audio

Android assets and resources Management API, plus audio management and some java io for advanced purposes. The Audio API can use the assets and resources. Audio, assets and resources can use java io.

The assets and resources API introduces a "resource_manager" and an "asset_manager" in the "App" that can be used to retrieve files or values from both resources or assets folder.

The audio API introduces Sound class representing a sound that can be play by a SoundPool or a MediaPlayer. The SoundPool is designed for playing small sound and can play different streams simultaneously and the MediaPlayer is prefered for long sounds or musics and can't play sounds simultaneously. Also the API provides 4 methods in "App" to get a sound from assets or from resources, and from a MediaPlayer or a SoundPool.

The java io part of this pull request is needed for some advanced use and is already improved by @xymus to help managing the Bitmaps.

Some classes are still only a wrapper to the Java class, this may be improved in a future version

Also modifying android_platform so the user can add his own resources in the android project without compiling it a first time. If there is a res folder in the 'nit part' of the project, it will rewrite the one generated by default by android. When the user adds it's own resources, he needs to create at least a "res/values/strings.xml" file where he needs to put a string resource with the name "app_name" and the value he wants.

The tests are implemented in the mnit_simple example application

Pull-Request: #543
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>