'Walk the ast tree for the python module.
Save submodule[.submoduleN][.identifier] into self.submodules
self.submodules will end up with tuples like:
- (\'basic\',)
- (\'urls\', \'fetch_url\')
- (\'database\', \'postgres\')
- (\'database\', \'postgres\', \'quote\')
It\'s up to calling code to determine whether the final element of the
dotted strings are module names or something else (function, class, or
variable names)'

def __init__(self, *args, **kwargs):

    super(ModuleDepFinder, self).__init__(*args, **kwargs)
    self.submodules = set()
