Python 3 compatibility

[jrm224]

A couple of methods that deal with config use the dict.iteritems() method which was removed in python 3. Seeing as python 2 reached eol a while ago now, it would be great to change that. I found this: https://www.python.org/dev/peps/pep-0469/ and this: https://stackoverflow.com/questions/30418481/error-dict-object-has-no-attribute-iteritems (these give conflicting answers to the question of what to replace iteritems with).
Thanks!

[stevemarple]

The code would certainly benefit from some changes to make it compatible with Python 3. I'd like to do that whilst maintaining Python 2.7 compatibility for as long as reasonably practical. Replacing

d.iteritems()

with

iter(d.items())

does do that.

[Linking to PR #8 where those changes have been made.]