Pagination error

[jcfrt]

While testing the dev branch I noticed a problem with pagination: the starting_after parameter keeps increasing, but never resets back to 0 which leads to incomplete data being returned after subsequent calls to that same method.

That is due to the fact that a python dictionary is defined as the default parameter in the _get_data method.
This is not a good practice (example reference) and should be set to None instead.

[MagerValp]

Fixed in #58 and #59