[#1] Fix {% url %} template tag compatibility with Django 1.5+

Use quotes for the url pattern name argument, 'django-counter-count', in
templates/counter/counter.html.

Add {% load url from future %} to ensure it still works with
Django 1.3 - 1.4.

(See https://docs.djangoproject.com/en/dev/releases/1.3/#changes-to-url-and-ssi)