Initial commit, based on the skeleton obtained from the tutorial at http://www.spectrumcoding.com/tutorials/android/2013/08/01/android-gl-box2d.html
Refactored  packages names to show more easily the code I did and the
code I used from a tutorial.

Created a SpriteObject class to draw sprites.
Done some tests over the character's movements.
Camera follows the character.
Improved character handling.
Added background to game, still improving its position.
Implemented character firing.
WIP in transparency of sprites. At the moment the bending function is
not the correct one, but at least we don't get the black square around
the sprites.
AliveObjects taking damage.
TODO Fix a bug on toasts, remove bullets after hitting.
Disposing of bodies removed from the scene.
Enemy autogeneration periodically.
Refactored many classes to clean the code a little bit.
Improved randomization of enemies and obstacles creation.
Added dummy AI to enemies.
Fixed firing height.
Fixed the game over process (only makes a toast and refills health).
Recreating textures after user locks screen. (only hero and bg).
Merged gitignore to use the github android one