This lets an application supply its own archivers, where they will work like
any built-in archiver. This allows abstract directory interfaces the same
way that PHYSFS_Io allows stream implementations.
This is a work in progress still. The API is still changing, and will remain
at version 0 until it is finalized (a theoretical future version 1 will be
for when the final public interface changes, not when we evolve the initial
API design).
Ryan C. Gordon
Aleksi Nurmi