[PATCH/RFC] submodule: fallback to .gitmodules and multiple level module definition

This patch series has two functional improvements for submodule

  - Fall back on .gitmodules if info not found in $GIT_DIR/config
  - multi-level module definition

Patches 1,2,4 is mainly code refactor but the second one also has some semantic change.

The other patches do the real functional changes.

Ping Yin (7):
      git-submodule: Extract functions module_info and module_url
      git-submodule: Extract absolute_url & move absolute url logic to module_clone
      git-submodule: Fall back on .gitmodules if info not found in $GIT_DIR/config
      git-submodule: Extract module_add from cmd_add
      git-submodule: multi-level module definition
      git-submodule: Don't die when command fails for one submodule
      git-submodule: "update --force" to enforce cloning non-submodule

 git-submodule.sh           |  326 ++++++++++++++++++++++++++++++++------------
 t/t7400-submodule-basic.sh |   31 ++++-
 2 files changed, 267 insertions(+), 90 deletions(-)