Consider handling arbitrary "stages" in the container

[ssnepenthe]

Right now there are pre-defined stages for activate, deactivate and boot.

It might be nice instead to handle whatever arbitrary stages the user can think of by passing non-existent method calls on the container to the invoke_on_providers method.

For example you might want to further divide boot logic: boot_admin, boot_ajax, boot_cron, boot_frontend, etc. Or maybe you might want a shutdown stage. What about uninstall?