improve compatibility for python 3

- correct .travis.yml
- make TransformerIterator iterable
- remove comparison "None > 0"
- use six.text_type instead of unicode
- use six.moves.input instead of raw_input
- use six.moves.reduce
- use operator module instead of lambda function
- integer conversion
- convert the pretrained test data
- remove some unused import
By curiosity, why 'latin-1'? I think we try to use 'utf-8' in general.