Make validator work with python2 and python3

[zimeon]

Have done a number of things including: use of relative imports, replace use of dict.has_key(key) with key in dict, change imports for things like urllib2 and BytesIO to work with both py2 and py3, additional decode('utf-8') to deal with bytes returns in py3, and significantly reduce the black magic for importing test modules (which didn't work in py3, now in TestSuite.__init__.

I have tested this as part of running the validator under py2 and py3 as I work on migrating https://github.com/zimeon/iiif/tree/image_api_2.1 to work with Image API 2.1 on both py2 and py3.

I bumped the version number to 1.0.1 and will update pypi when we agree things are good.

[azaroth42]

Verified locally with 2.7 👍

[zimeon]

Have packaged and updated on pypi. My IIIF library code now uses the pypi packages to run tests in py2/py3 on travis. All seems good.