Aplicando eventos del ciclo de vida en Asteroides

On branch master
modified:   gen/org/example/asteroides/R.java
new file:   res/raw/audio.mid
modified:   src/org/example/asteroides/Asteroides.java
modified:   src/org/example/asteroides/Juego.java
modified:   src/org/example/asteroides/VistaJuego.java