Full python 3 compatibility

[smiley]

Some of the code -- as shown in #16 -- doesn't work in Python 3.x, while some doesn't act as expected. This includes:

• Calling dict.keys() in returns a dict_keys object that can't be accessed by-index. (TypeError when calling usr.friends #16)
• Float division in errors.py:76 causing all checks in raiseAppropriateException to fail and, consequently, raise a debug exception thrown by debug.no_return.
• Name-encoding in SteamObject.__repr__ causes the resulting string to be a bytes object instead and end up ..."b'Smiley'"... instead of ..."Smiley"....
• Use range instead of xrange (xrange became range on 3.x, theoretical performance changes on 2.x are acceptable)

This needs to be fixed as soon as possible, since Python 3 is very much in use and considered standard Python.

[juanchristian]

You're fast, thanks!

[jleclanche]

Update on this PR? Do you guys need help?

[smiley]

What I mentioned above I fixed already, but I'm keeping this open for any other Python 3.x issues I might come across.

[smiley]

Closing for now, as (it looks like) nothing else broke in Python 3.