function made to compute the histo of the a slinding kurtosis to detect bad
signals, a lot has still to be done on that, big potential. This function
should be use on trace big enough to be statistically realistic

Input:
trace: trace to be processed
first_sample & last_sample: window to be processed
kurto_sample : window size counted in samples to process the kurtosis
pivot_value : value from which to compute the standard value (usually 1.5)

Output:
ratio_low: ratio of samples under the pivot_value / total number of samples
std_value: 68