make icdiff compatible with python3 (as well as python2)

The only changes needed, I think, were parentheses around
print statements and // for truncating division.
Tested on python3.4, python2.7, and python2.6 with jefftk's
example files:

button-a.css
#input, #button {
  width: 350px;
  height: 40px;
  margin: 0px;
  padding: 0px;
  margin-bottom: 15px;
  text-align: center;
}

button-b.css
#input, #button {
  width: 400px;
  height: 40px;
  font-size: 30px;
  margin: 0;
  padding: 0;
  text-align: center;
}