Inspects, updates and manages submodules.

# To install a repository's specified submodules:
git submodule update --init --recursive

# To add a git repository as a submodule:
git submodule add <repository_url>

# To add a git repository as a submodule at the specified directory:
git submodule add <repository_url> <path/to/directory>

# To update every submodule to its latest commit:
git submodule foreach git pull