Merge branch 'ar/submodule-add-more'

More parts of "git submodule add" has been rewritten in C. * ar/submodule-add-more: submodule--helper: rename compute_submodule_clone_url() submodule--helper: remove resolve-relative-url subcommand submodule--helper: remove add-config subcommand submodule--helper: remove add-clone subcommand submodule--helper: convert the bulk of cmd_add() to C dir: libify and export helper functions from clone.c submodule--helper: remove repeated code in sync_submodule() submodule--helper: refactor resolve_relative_url() helper submodule--helper: add options for compute_submodule_clone_url()