Write a tree builder based on built-in xml.sax.handler

[Leonard Richardson]

https://bugs.launchpad.net/beautifulsoup/+bug/1417011/comments/4 contains a request to make it possible to parse XML into a Beautiful Soup parse tree without installing any third-party libraries. This should be possible using the xml.sax.handler library (https://docs.python.org/2.7/library/xml.sax.handler.html#module-xml.sax.handler).

I don't have any plans to implement this, but it's a reasonable request (especially for platforms like Windows where installing lxml is difficult) and I want to track it separately from bug 1417011, which is a problem with lxml.