Change dfu.py to be Python 2/3 compatible

* Chane dfu.py to use Python 3 syntax to avoid dependency on Python 2.
* Update Makefile to call python instead of python2
* Fix #33
Merge pull request #45 from iabdalkader/master

Change dfu.py to be Python 2/3 compatible
Merge remote-tracking branch 'upstream/master'