devel/appstream: New port - Provides a standard for creating app stores

AppStream is a collaborative effort for making machine-readable software
metadata easily available to programs that need it. It is part of the
Freedesktop ecosystem and provides a convenient way to retrieve information
about available software.

AppStream consists of a specification to describe individual software
component metadata in XML (so-called MetaInfo files), as well as a
derived specification for a metadata-collection format to provide a
list of these metadata entries in XML or YAML for easy consumption by
software centers and other tools which need to know about available
software in a repository.

WWW: https://www.freedesktop.org/wiki/Distributions/AppStream/

PR:		258541
Original by:	Olivier Duchateau <duchateau.olivier@gmail.com>