Update native library to Coremod 4.2.1

Coremod is a lightweight version of libxmp. This version updates the
old xmp 3.3.0 code previously used in the AndEngine MOD player extension.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Add Soundtracker loader to Coremod player

Regular Coremod supports Protracker, Scream Tracker 3, Fast Tracker II
and Impulse Tracker modules, which are in practical terms the only
relevant module formats today. The AndEngine modplayer extension example,
however, uses an Ultimate Soundtracker module. So to keep the example
working, add Soundtracker support to Coremod (it was written to be
embeddable and modular anyway).

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update to Coremod Java API

Update Xmp classes to the new Coremod Java API files, keeping the
previous AndEngine modplayer API intact.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Remove binary file from repository

libxmp.so is a generated file and shouldn't be in the git repository.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Update modplayer extension API

This is a proposed update for the modplayer extension API. The following
changes were made:

1 - To be consistent with getTime(), seekTime() is changed to milliseconds
2 - A few methods were renamed to more meaningful names, such as
    getPattern() instead of getPlayPat()
3 - Added methods to set/get the master volume

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>
Use initialization-on-demand holder

Change singleton creation to use the Initialization-on-demand Holder
pattern, which allows safe lazy initialization with good performance.

Signed-off-by: Claudio Matsuoka <cmatsuoka@gmail.com>