appdata: Add <releases> section

[wjt]

[tomreyn]

Thanks for your efforts, wjt.

I agree that release / version information is nice to have in the appdata. However, just adding it as it is would also mean adding yet another step to an already very long list of things-to-be-manually-done-during-release (otherwise it would get outdated and would look stale soon). I haven't thought about this more, but maybe it could be possible to automate updating this file with the latest release changelog. If we had this, I would be in favor of having release info on the appdata file.

[wjt]

How do you generate the current change log? I believe there are scripts which generate news files from appdata floating around.

[tomreyn]

The changelog is updated manually just before release (in git, in the megaglest-source repository).

[wjt]

wjt@toolbox:~/src/MegaGlest/megaglest-data☭ appstream-util appdata-to-news others/appdata/megaglest.appdata.xml
Version 3.13.0
~~~~~~~~~~~~~~
Released: 2017-03-09

The MegaGlest team is proud to release v3.13.0. Notable improvements to this
release include:
 * Multi-building select and key-binding for production of units
 * Buildings of the same type can be added to a control group, which means
   multiple units can be produced with a single click
 * A crash (out of sync) that sometimes happened when playing with Fog-of-War
   disabled has been fixed
 * Improved AI behavior
 * To help keep multi-player games more balanced and to ensure that players are
   practiced enough to harvest resources and beat a normal CPU, a scenario is
   automatically launched the first time a user tries to enter the lobby. The
   scenario must be won before the player can actually enter the lobby.

[wjt]

So what I am proposing is: make the appdata file the canonical source for the changelog, and generate the plain-text version at release time using appstream-util appdata-to-news.