Py3tftp

- Fix timeout interval handling (many thanks pkropine) - https://github.com/sirMackk/py3tftp/pull/17

- Improve filename sanitize to work on Windows (many thanks pkorpine) - https://github.com/sirMackk/py3tftp/pull/15

- Change logger to module logger (thanks schrd!)
- Add flake8 to tests; Fix style issues; Make travis fail on test errors.

- Adds windowsize option handling for RRQ (many thanks jpmzometa!)
- Adds tsize option for RRQ (thanks schrd!)
- handle error packets if client aborts RRQ transfer (thanks schrd!)

- Fixes RRQ not waiting for ACK of last package (thanks jpmzometa!)
- Adds netascii support (thanks keenser!)

- Fixes KeyError bug with the `-l` CLI option (thanks pritstift!)