Un ListView que visualiza Layouts personalizados

On branch master

modified:   gen/org/example/asteroides/R.java
new file:   res/drawable-hdpi/asteroide2.png
new file:   res/drawable-mdpi/asteroide2.png
new file:   res/drawable-xhdpi/asteroide2.png
new file:   res/layout/elemento_lista.xml
modified:   src/org/example/asteroides/Puntuaciones.java