- Use a define for the so version and fix -devel requiring the old libappstream3

- Update to version 0.10.0
- Disable stemming support until we have libstemmer packaged.
- Generate libappstream4 packages since AppStream changes the ABI in 0.10.0
Notes:
* This release breaks API/ABI in order to support multiple metadata sets describing the same
component (needed for bundling support), moving away from the database as central data store
and general cleanup.
* Porting is relatively straightforward, if you were using AsDatabase, you should switch to AsPool
now (AsDatabase has been a wrapper around AsPool for a while anyway).
* Many methods became private API with this release, file a bug if you miss anything.
* The 'categories.xml' file is gone - please account for that if you were reading it directly,
and consider using AsCategory instead, which offers the same functionality.
Features:
* Remove the AsDatabase class (Matthias Klumpp)
* Use cmakedefine for compile-time features (Matthias Klumpp)
* Rename AsDataPool -> AsPool (Matthias Klumpp)
* Add placeholder enum for web applications (Matthias Klumpp)
* qt: Implement Appstream::Release for the Qt interface (Aleix Pol)
* Recognize the "Pantheon" desktop for Elementary (Matthias Klumpp)
* Get rid of the menu parser and make AsCategory more useful instead (Matthias Klumpp)
* Allow AsComponent to automatically check for list-value duplicates (Matthias Klumpp)
* Give bundles their own class (Matthias Klumpp)
* Stop shipping the categories.xml file (Matthias Klumpp)
* Allow multiple metadata sets in the pool to describe a component (Matthias Klumpp)
* Name AppStream metadata styles consistently (Matthias Klumpp)
* Allow the 'C' description fallback to be turned off (Iain Lane)
* Make AsScreenshot return localized images by default (Matthias Klumpp)
* Allow to compare AsRelease versions easily (Matthias Klumpp)