Filter queryset feature to generic view

Hi there,

First of all thanks for this great app!

I use django_tables2 in one of my projects and needed a search feature so I tweaked the generic view to add a "search_fields" attribute, similar to the list view in django admin. I was wondering if you'd be interested in having this feature merged in.

I also built this on the generic view level instead of making it a proper feature of the table itself. If you are interested in the general idea, I'd be more than happy to work on it (tests and docs included ;).