Python 3 Compatibility

[stevencox]

FYI, I was able to use this repo with Python 3 by changing these changes:

1. imports

#from cStringIO import StringIO                                                                                                                                                                                                               
try:
    from StringIO import StringIO
except ImportError:
    from io import StringIO

import datetime
import urllib
#import urlparse                                                                                                                                                                                                                              
import urllib.parse as urllib

2. unicode -> str

        elif response['content-type'].startswith('application/sparql-results+json'):
            # See http://stackoverflow.com/a/19366580/2276263                                                                                                                                                                                 
            # for justification of unicode() below                                                                                                                                                                                            
#            return simplejson.loads(unicode(content, "utf-8"))                                                                                                                                                                               
            return simplejson.loads(str(content, "utf-8"))

Relatively untested, but potentially helpful as a start.