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.)

The time series (and some extra stats) of a single benchmark
is now available in a separate, stand-alone URL.