This update for libmodulemd fixes the following issues:

- Added support for 'buildorder' to Packager documents
- Fixed an issue with ModuleIndex when input contains only Obsoletes documents
- Extended read_packager_[file|string]() to support overriding the module name and stream
- Ignore Packager documents when running ModuleIndex.update_from_*()
- Added python overrides for XMD in PackagerV3
- Added python override to ignore the GType return when reading packager files
- Added PackagerV3.get_mdversion()

This update was imported from the SUSE:SLE-15-SP2:Update update project.