Fix an issue when calling `get_services()` in Python 3.

(This now matches the response decoding already used in `_get()`. It was never noticed because tests didn't cover it.)
Increase test coverage. Reorder imports so that Python 3 is first.
Tests - add mocking to test `get_services()`

This may be overkill but it does increase test coverage and if we develop more fine-grained tests for `_get()` in the future, mock will help.
Use `2to3` automatically during the build process.

It doesn't make a ton of changes in truth, but it's a recommended step on the conversion path. It does handle the `urllib` path though!
TravisCI - let's see if it will use `setup.py test` and thus install the test dependencies