improved nested list management

@superalex

I see your #3 PR and raise it by one with this :-)

What you in fact discovered was a full grown up bug. In this PR, I fix that bug so nested list are correctly managed within the `build_params_tuple` method, and that indeed covers your use case. 

Anyway, I'd like to get your opinion. If you feel your PR covers something mine don't please tell me. If you could also be so gentle as to test this one with your particular use case, I would really appreciate.


btw and off-topic, do you have any comments regarding the documentation? I'd like to get some feedback on that.


PS: txs for helping!!