Django 1.6

Ported to support Django 1.6, in which the underlying caching API has changed. See https://docs.djangoproject.com/en/dev/releases/1.6/#miscellaneous.

To support both Django 1.6 and < 1.6 simultaneously, a new constant, `DEFAULT_TIMEOUT`, was added to replace the use of the `None` timeout value. This is consistent with how caching works in Django 1.6. Part of this porting also fixes #44.

Updated the documentation accordingly, and added some points on changing timeout values, including the previously undocumented `NO_CACHE`.