This commit improves the definition of the stability scores (LCSS and LCSSE) of the last change in a time series in several ways. The definition of a change in itself is also improved: Now the search for the next change compares each candidate against a fixed base value (i.e. the one at the previous change snapshot) instead of against the value at the preceding snapshot. (The latter algorithm would never detect any change in a time series that changed in small increments over time.)