In order to create an element with an attribute and a child, this is
necessary:

    e = Element("foo")
    e.setAttribute("bar", "baz")
    e.appendChild(quux)

It would be preferable if Element.__init__ accepted two additional
parameters to shorten this:

    e = Element("foo", attributes={"bar": "baz"}, children=[quux])

It may also be preferable to have a third new parameter, attributesNS,
to parallel the Element.setAttributeNS method.  This would accept a dict
mapping namespaceURI and qualifiedName to an attribute value.