Better docs using GitHub pages

[ericoporto]

It would be nice to leverage GitHub pages to add some better docs here. Could use something like Sphinx to build from markdown.

[ericoporto]

Started to work on this, the idea is to have cli documentation, gui documentation, the concepts used in agstoolbox (managed vs unmanaged and others) and common work processes - building and releasing a game, upgrading AGS editor, upgrading a project (loading with a newer editor).

With these last one I hope by writing things down I can figure out better ways to support these stuff in the tool.

So far most of my development has been thinking about the command line interface since I have been using that more actively in many ci pipelines. So perhaps writing something about that could be useful too.