These benchmarks are now more useful for seeing how these B-trees perform.
In plot.py/plotmpl.py:
- Added --legend as another alias for -l, --legend-right.
- Allowed omitting of datasets from the legend by using empty strings
in --labels.
- Do not sum multiple data points on the same x coordinate. This was a
bad idea that risks invalid results going unnoticed.
As a plus multiple data points on the same x coordinate can be abused for
a cheap representation of measurement error.