Add support for needed real life features

[tasn]

This pull request adds two things.

1. Support for sending data without limiting to the "msg" field which is not really needed.
2. Support sending bulk messages on a queryset. Sending to an unlimited amount of objects in an efficient way.

These are needed in order to use this framework, as they are both very common real-life use cases.

Note: if you wish, this merge commit can be dropped, and you can just use the 2 commits themselves, as they are not tightly tied.

[tasn]

Would you like me to update the pull request? Or will you just add the changes in the merge?

[bogdal]

@tasn yes, please update this PR.

[tasn]

I changed the PR as requested. While it mostly preserves behaviour, it still changes behaviour when a dict is passed. Before this PR passing a dict would translate to "msg: {...}", now it's flat.

[tasn]

Updated the var names too.

[bogdal]

Thanks

[tasn]

Cool, thanks.