Add support for exporting multiple notebooks

[lresende]

Add support for exporting multiple notebooks by providing multiple --export parameters.

Fixes #3
Closes #5

[sourav-mazumder]

Hi Luciano,

To answer your Qs on how the multiple notebooks communicate each other, there would be two choices -

1. Either they store the results in intermediately in a File SErver/Object Store/Databases
2. Or they create the model and save the Model

Essentially a use case is in this case realized through use of multiple notebooks where each notebook takes care of one independent step/module. This helps in maintainability of the code as well as possible reuse.

Regards,
Sourav