Release Notes referring to non-existing versions from the past

[Ulrich Windl]

This was changed since 5.18 (now for 5.19): The Release Notes (CHANGES) describe versions that did not exist as such, for example "5.13.0" and "5.16.0" never existed (but "5.13" and "5.16" did). Probably this bug was created by an overly eager find and replace ;-)

[Tildeslash]

We have originally used x.y[.z] version scheme, which was confusing for some users, as they interpreted version like 5.17 as 5.1.7.

To make sure the version is number is clear, we have switched to x.y.z versioning, including changelog of older "x.y" style versions. The "x.y" is identical to "x.y.0".