AppData additions required for the software center

[Richard Hughes (semi-automated)]

Hi again!

First, apologies for the direct email. I'm emailing you directly as you've been 
listed as the update contact in one or more AppData files.

We've been busy building an awesome software center, and we've been adding more 
and more metadata fields that upstream authors can set. The software center is 
now being used in Fedora, Opensuse, Ubuntu, Debian and Arch, with many millions 
of happy users.

Some of the newest features include a way to make it easy for translators to 
contribute new translations of your applications by specifying a URL in the 
pspp.appdata.xml AppData file that tells them where to start looking. This can 
be specified by adding:

<url type="translate">http://the-web-site-with-translation-instructions/</url>

Another useful tag to add is to tell end-users where to donate, for instance:

<url type="donation">http://www.gnome.org/friends/</url>

Also, by including keywords into either the desktop file or the AppData file 
you can increase the number of search matches you get in the software center. 
Adding application-specific keywords like "editor" or "vhdl" means that we can 
provide better search results for common queries. Keywords are also stemmed, so 
searching for "edit" will also match "editor" and "edits" so there's no need to 
add every variant. You can add keywords using:

<keywords>
  <keyword>something</keyword>
  <keyword>anotherthing</keyword>
</keywords>

If it's been some time since you updated the AppData file (and hey, you've got 
an app to write!) you can get add the latest metadata fields by doing 
`appstream-util upgrade pspp.appdata.xml` and then replacing any FIXMEs in the 
file with actual data. We'll be putting more functionality into the software 
center in the future that uses this extra data, but we need more upstream 
software to opt-in before we can enable features, for instance, providing a 
button for users to donate to specific apps.

You can also use `appstream-util validate-relax` on your AppData file to check 
the various fields meet our style guidelines. If you disagree with any of the 
validation warnings, please let me know!

Of course, you don't have to do a release with these enhancements straight 
away, and if you have a stable branch it would be a good thing to backport this 
as well if it does not add translated strings or you have no string freeze 
policy.

When you've changed the file(s) and committed, please email me back and I'll 
mark your application as completed. If you don't want to hear from me ever 
again just edit the <update_contact> in the AppData file and change it to 
somebody else. I'm not planning on emailing more than once every 6 months, so 
don't worry about me spamming you with even more work to do.

Thanks,

Richard