Support Python 2.7 and Python 3 winreg imports on Windows

[tracyde]

Wraps the winreg import in a try statement in order to gracefully support the _winreg -> winreg name change from Python 2.7 to Python 3.

try:
    import winreg
except ImportError:
    import _winreg as winreg

[apprenticeharper]

The master branch is currently Python 3.x only.