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
From the code it looks like `n` is, but `pool_size` is a user-provided variable, and there are no checks anywhere that it is integer, so it could be anything. Either way, this is in a method which is only made for unit tests, so both `//` and `int()` are fine with me.