This major refactoring of the catalog based shell utilizes the new API macro and
the API Schema as well as rustyline instead of the old GNU readline C API.
The code now has these 3 main components:
* The `Shell` which handles the readline loop via rustyline.
* The shell functions defined via the API macro.
* The `Context` which holds catalog and decoder instances.
Signed-off-by: Christian Ebner <c.ebner@proxmox.com>