[physfs] Adding Support for Custom Archives

[Ryan C. Gordon]

> There isn't anything wrong with that (my engine is free), but it makes
> it more difficult to work with and distribute. For example, I must
> debianize the physfs source, I need to learn mercury to patch it, I must
> add the augmented libphysfs package into my apt repository, and I must
> find a way to reconcile libebml (C++ based) with the source.

You could just include the PhysicsFS source with your project (this was 
the intention, as most targets don't have the luxury of relying on a 
Debian package).

> Does anyone have any recommendations? Ideally, all I'd need to do is
> provide the necessary callbacks at runtime for whenever an archive of my
> custom type is accessed.

One of the goals for PhysicsFS 2.1 is to allow for external archivers, but 
this work hasn't started yet. I'll probably spend time doing major updates 
to PhysicsFS in a month or two after things calm down around my house.

--ryan.