Convert a URL into it's response (a *str*).

def _get(url):
    """
    Convert a URL into it's response (a *str*).
    """
    if PYTHON_3:
        req = request.Request(url, headers=HEADER)
        response = request.urlopen(req)
        return response.read().decode('utf-8')
    else:
        req = urllib2.Request(url, headers=HEADER)
        response = urllib2.urlopen(req)
        return response.read()