Request: new load syntax for _not_ cloning submodules

[AndydeCleyre]

A plugin/repo's submodules are not always needed for regular use, and in those cases, refraining from cloning them can save the user some space and bandwidth. A new syntax like zgen load --no-submodules... could be handy.

[jandamm]

Hi, I've created a maintained fork of zgen - dubbed zgenom - which fixes some bugs as well as introducing new features. Please let me know what you think of my solution.