Errors thrown via errback being logged properly now.
Now a param in request.kwargs is only a list if is really a list coming.
Merge pull request #83 from nicholasamorim/request_kwargs_fix

Now a param in request.kwargs is only a list if is really a list coming.
Merge pull request #80 from nicholasamorim/fix_error_log

Errors thrown via errback being logged properly now.
Added support to fields and exclude when serializing to dict or json
Removed clutter and added parameters in the function docstring.