Ideas for improving addon packaging

[Frostwithasideofsalt]

1. rename addon package file extension from .zip to a custom one
   They would probably just be zip files with a new file extension, which seems kinda pointless at first, but consider this;
   -you could set it so this file format is opened by supertux by default, meaning you would just have to open the file in the file explorer to install the addon
   -makes installing addons more dummy proof, as now the thought of extracting the zips contents and putting it somewhere has been eliminated.

2. nfo files are already a file extension used in windows, which for some reason sometimes results in you needing 7zip to zip up an addons contents, and it makes editing the contents of a supertux nfo file much more inconvenient