Refs #15 - Permits to caches templates loaders by accepting 'complex' sequences, ie: https://docs.djangoproject.com/en/1.6/ref/templates/api/#django.template.loaders.cached.Loader.
Refs #15 - Added a test around Django's TEMPLATE_LOADERS.
DjangoSettingsSchema.TEMPLATE_LOADERS now accepts strings and tuples (was: strings only). Closes #15.