urlize and urlizetrunc template filter docs need expansion

[Gabriel Hurley]

I was looking at the source code for the urlize filter today and realized the following:

1. The docstring for the urlize has much better documentation than the reference docs do.
2. The autoescape keyword argument to both the urlize and urlizetrunc template filters is not documented.
3. The limit argument to urlizetrunc isn't explicitly documented and needs an example.
4. The the nofollow argument to django.utils.html.urlize is always passed as True by django.template.defaultfilters.urlize and django.template.defaultfilters.urlizetrunc. While this is a good default, it definitely needs to be documented.

All of the above needs to be incorporated into the docs for those two filters, and they need both more and better examples.