unbind API

[cgarciae]

As suggested in #2394 (comment), its currently not clear for users that clone produces an unbounded copy of the module. To get hold of a submodule and its variables you currently have to use this pattern:

module, variables = load_module()
bounded_module = module.bind(variables)
submodule = bounded_module.some_submodule.clone()
submodule_variables = bounded_module.variables

The new proposed .unbind() method provide more clarity on how to do this process:

module, variables = load_module()
submodule, submodule_variables = module.bind(variables).some_submodule.unbind()

Signature could be:

unbind(self, **clone_kwargs) -> Tuple[Module, FrozenVariableDict]

cc @jheek

[marcvanzee]

How about unbind()?

[marcvanzee]

@cgarciae Just so you won't be confused, I renamed the issue "snapshot API" --> "unbind API"

[cgarciae]

Perfect, edited the original comment with the new name.