report both the previously installed version and the updated version after an update

[Mithgol]

Checklist

• I'm reporting a feature request
• I've verified that I'm running youtube-dl version 2019.09.28
• I've searched the bugtracker for similar feature requests (including closed ones) and haven't found any similar ones

Description

Currently youtube-dl -U reports only the latest version, either as the up-to-date version (such as “youtube-dl is up-to-date (2019.09.28)”) when an update is not necessary or as the version being installed when an update happens.

However, in the latter case the reported version is not enough for the comfortable reading of the changelog. I'd like to know where exactly should I stop reading the changelog, and thus I have to request the previously installed version to be also displayed after an update.

(Currently, as a workaround, I make sure to always run youtube-dl --version before I run youtube-dl -U, but that's twice longer than it should be.)

[basicmaster]

Some time ago I opened #18451 for this.