modelviews: use modelform_factory instead of doing it by hand
add modelviews.ActionEndpoint
refactor modelviews and add better docs

Changes to the modelviews include:

* URL keyword argument is 'pk' by default and can be overridden
* DetailEndpoint has only get_instance; get_query_set removed
* misc fixes
tests: silence intentional warnings
updated copyright and made the authors list explicit
improve docs