Implement select_sorting_periods

[alejoe91]

Slices a sorting object based on an array ov valid periods. Periods are defined as a structured dtype as:

base_period_dtype = [
    ("start_sample_index", "int64"),
    ("end_sample_index", "int64"),
    ("segment_index", "int64"),
    ("unit_index", "int64"),
]

[samuelgarcia]

I want to have this in NumpySorting since long time. We could move it there no ?

And also you can do a np.searchsorted for segment at once. without any loop.

[samuelgarcia]

This is OK for me.
Make a clear documentation somwhere woule help ?