[Feature Request] Adding before/after columns in the summary table

[chixiangzhou]

The current pycobertura diff report only shows the diff part (e.g, diff miss, diff coverage), which might cause some confusion without knowing the before/after coverage info.

It would be nice if we can also show the coverage info in the summary table before and after the changes were introduced.

[gro1m]

@loganharbour Is this related: #117?