Support Python 3

• Runs the first stage of the futurize command. The following changes are made
  • print a, b -> from __future__ import print_function ... print(a, b)
  • insert from functools import reduce
  • raise ValueError, 'message' -> raise ValueError('message')
• Fix mixed indentation in options/Gauss/patchUpgrade1.py (tab -> 8 spaces).
• Add Python 3 syntax check in CI