Add an option to filter api urls in DocumentGenerator

[swistakm]

Maybe using django url namespace? It could be parameter of .get_docs method. It would be nice feature to have separate docs for different versions of API and I think that using different namespaces for different API versions is good way to achieve this.

There could be also other kinds of filters e.g. regex.

[marcgibbons]

This is a good idea. Right now, it's possible to specifiy which URL patterns to document by providing them in the constructor when instantiating the DocumentationGenerator class. I will have a look at your pull request in the next few days. Thanks for your help and interest!