's1 - s2 -> remove keys in s2 from s1.
Examples
>>> s1 = Struct(a=10,b=30)
>>> s2 = Struct(a=40)
>>> s = s1 - s2
>>> s
{\'b\': 30}'

def __sub__(self, other):

    sout = self.copy()
    sout -= other
    return sout
