Streaming parser

[mvz]

Someone asked whether happymapper could be used with a SAX parser for cases where the XML is big. I then thought it would be difficult, especially in cases where attributes are defined with xpath expressions.

I'm opening a ticket here to keep track of this and see if the difficulties can be overcome.

Regardig streaming xpath expression evaluation, there is https://github.com/StevenLooman/saxpath for JavaScript, with the main algorithm in https://github.com/StevenLooman/saxpath/blob/master/lib/saxpath.js, and https://github.com/jaxen-xpath/jaxen for Java. And perhaps https://github.com/jmosser-NISC/scireumOpen/tree/master/src/com/scireum/open/xml.