testing xrange->range fallback for python 3
using 'range' instead of 'xrange' in game.py

Since we're using it only once and on a small range, it's cleaner to do
that than keeping the try/except hack to use the good function depending
of Python version and testing it.
testing clear/cls during game loops
game.loop now returns the final score.
^C tests for term2048.game