Add Python 3 compatibility

[RobLoach]

Aim is to allow running in either Python 2 or 3. Still some things missing:

• PySteam Python 2/3 Compatibility
• Fix return sum(map(self.roms_for_console, consoles), []) in rom_finder.py since map() now returns an iterator
• Check if if not instances in settings.py in Python 3 actually works on map() iterators
• See what's missing from Python 3 support #268

Would appreciate some testing, et al.

[scottrice]

Oof. I think this is a sign that I need to convert over to something like requests.

[scottrice]

I know I said it on the pysteam pull request as well, but thanks for doing this. I'll try to take a look sometime soon. The big thing I need to solve before I merge this is I need to figure out how to make sure I dont break it as soon as I write another line of code :P.

[RobLoach]

Agreed, making sure the compatibility works in Pysteam is the first step. I saw some work had gone into this before as well.