Add from_input in Rdf_xml.
Created by: flh
Xmlm allows one to set some options for reading XML input streams as optional arguments of Xmlm.make_input.
This patch adds a Rdf_xml.from_input function which populates a RDF graph from a Xmlm.input handle, allowing one to completely customize how Xmlm reads XML data.
This is in particular useful when parsing XML files which declare named entities in their DTD: Xmlm does not parse these declarations, but we can workaround this limitation by using the ?entity argument of Xmlm.make_input.