Text delta summary report builder

[manfred-brands]

Fixes #534

Creates a delta coverage report based upon the last two historic coverage files:

Delta Summary
  Generated on: 18/07/2022 - 16:24
  Description          Previous             Current              Delta
  Coverage date:       18/07/2022 - 11:39   18/07/2022 - 16:24
  Line coverage:            77.2%                77.5%          000.3%
  Covered lines:            3,976                4,039              63
  Coverable lines:          5,145                5,207              62
  Total lines:             15,190               15,639             449
  Covered branches:           952                  966              14
  Total branches:           1,270                1,284              14
  Covered methods:            605                  619              14
  Total methods:              795                  809              14

[danielpalme]

Thanks for your PR. I will definitely review and merge it.

But it will take some time, since I'm really busy at the moment.