docs: annotate the v4 API

docs: annotate the v4 API

Namely:
 - kmod_config_get_aliases
 - kmod_config_get_blacklists
 - kmod_config_get_install_commands
 - kmod_config_get_options
 - kmod_config_get_remove_commands
 - kmod_config_get_softdeps

 - kmod_config_iter_free_iter
 - kmod_config_iter_get_key
 - kmod_config_iter_get_value
 - kmod_config_iter_next

 - kmod_dump_index

Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Link: https://github.com/kmod-project/kmod/pull/128
Signed-off-by: Lucas De Marchi <lucas.de.marchi@gmail.com>