Py3k: seedlink `futurize -0 -w .`
Py3k: seedlink, fixing obvious issues

Checked compatibility with
* tests/example_SL_Hello.py
* tests/example_SL_RTTrace.py
* tests/test_slclient.py

All of those do not raise errors any more. However, I am waiting for ever
for data :\.
Py3k: seedlink, flake8'tifying