Part of the effort to reduce dependency on the py library.
Besides that, py.xml implements its own XML serialization which is
pretty scary.
I tried to keep the code with minimal changes (though it could use some
cleanups). The differences in behavior I have noticed are:
- Attributes in the output are not sorted.
- Some unneeded escaping is no longer performed, for example escaping
`"` to `"` in a text node.
Ran Benita