Store metadata within app package (feature request)
The Pyxel application file (.pyxapp) provides a convenient way to distribute and play Pyxel applications. In practice, it is a zip archive of the application files with a special file pointing to the startup script.

For a convenient way to archive and manage a collection of application files, I would suggest adding a metadata file inside the application file (maybe something like `pyxapp.toml`? [toml](https://toml.io/) seems to be quite popular among Python developers these days) to provide some metadata about the application. I was thinking about:
 - title
 - author
 - description
 - webpage/url
 - version
 - license
 - screenshot/gif animation provided in the pyxapp file itself
 - *etc*

Of course the authors are free to provide whatever metadata they see fit. The point of specifying the format is to ensure compatibility and promote usage. The pyxel web player could then also display this information along with the application when playing it.
