#106 Function to get samples

A really easy function get_sampler that calls the sampling method, and converts the output into the specified format. If an analyzer, of type AnalysisCallback is provided, then the performance attributes are also computed and combined.

There is an example on the Semiramis notebook.

In case, I did some more changes to the sampler, as I realize that the seed was initialized at the beginning, and the sampler was creating every time with the same seed, hence it was always providing the same samples. Now, we store sampler_prev, and if no sampler is provided, and the strategy and the engine are the same, then we reuse the previous sampler.