read url_extra_kwargs from templatetag

I was trying to use `url_extra_kwargs` in my project, and found that this was getting passed to `BootstrapPaginationNode` and `BootstrapPagerNode` as a string (keywords and args together). Not knowing a better way to pass a dict from template to django, I tweaked the code with 

     import ast
     ast.literal_eval("{'my_kwarg':12}")

type munging. This was helpful to me, so I wondered if it might be helpful for you. 

Great app btw!