* calculate the number of changes files and insertions and deletions between two tags (or branches):
git diff --stat 2.6.0 2.7.0 | tail -n1

* calculate the number of commits between two tags (or branches):
git log 2.6.0..2.7.0 --oneline --no-merges | wc -l

* use https://www.timeanddate.com/date/duration.html to calculate the number of dates between the announcements for major releases

* Results:

release files_changed insertions deletions commits days
2.1 528 147256 29568 546 644
2.2 188 31427 2599 232 156
2.3 217 19157 6568 310 116
2.4 421 30452 12030 780 260
2.5 875 75135 29508 1807 438
2.6 698 69462 18826 1150 302
2.7 356 168107 9176 476 188
2.8 563 54361 13968 867 328
2.9 1267 110465 53298 1886 594
