Use "mild outliers" method to remove exceptional speed-ups and slow-downs
from the graph, so that the majority of information is not lost by the
scaling. Add the timing labels to the bars so that the true factor is
always presented.
cairo-perf-chart takes multiple runs (currently it is limited to
prefiltered data sets) and pretty-prints a chart showing performace
improvements/regressions (in either ASCII or HTML) along with a
cairo-perf-chart.png
