First pass at Python 3 compat
Added skips to directory snapshot tests on Windows since Windows does not have the ability to detect renames using the directory snapshot util
Updated .travis.yml to test against Python 3.x
Changed unicode_paths to only use positional arguments for Python 2 compatibility
pass encoded path to os.path.isdir et.al. as they do not use a fallback encoding and will fail if locale is C and path unicode.