's + s2 -> New Struct made from s.merge(s2).
Examples
>>> s1 = Struct(a=10,b=30)
>>> s2 = Struct(a=20,c=40)
>>> s = s1 + s2
>>> sorted(s.keys())
[\'a\', \'b\', \'c\']'

def __add__(self, other):

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