Compatibility with Python 3.x

I've only run tests against 2.7 and 3.3 (travis-ci is pretty slow right now...).
2.7 passes all tests, 3.3 is failing one:

```bash
FAIL: test_template_escape (test_utility.TestUtility)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/jiawei/Code/underscore.py/tests/test_utility.py", line 168, in test_template_escape
    self.assertEqual(tmpl(), '<p>\u2028\u2028\u2029\u2029</p>')
AssertionError: '<p>â\x80¨â\x80¨â\x80©â\x80©</p>' != '<p>\u2028\u2028\u2029\u2029</p>'
- <p>â¨â¨â©â©</p>
+ <p>    </p>
```

Seems like the paragraph and line separators are causing some issues in 3.x - hopefully you can help patch the issue :)
Everything else seems to be working fine!