Add support to python 3

[maxiplux]

My friend thanks for this amazing library , but please would be possible add support to python 3. I think that is only change iteritems by items() , return Bunch( (k, bunchify(v)) for k,v in items(x) ) . thanks

[jaraco]

Dupe of #17

[dachshund-digital]

Come on... Python2 is DEAD, not supporting Python3, really? Crashes in python3...

AttributeError: 'dict' object has no attribute 'iteritems'

[mnaielksu1]

I did the following changes in /python3.8/site-packages/bunch/__init__.py to support Python3: Line 245: return Bunch( (k, bunchify(v)) for k,v in x.items() )
Line 270: return dict( (k, unbunchify(v)) for k,v in x.items() )

Now from bunch import bunchify is working.