make `no_network` configurable

[rlskoeser]

I'd suggest adding it as an argument to the functions that call etree.parse, and then passing it through to that call:

neuxml/neuxml/xmlmap/core.py

Lines 54 to 57 in 992ff81

	def parseUri(stream, uri=None):
	"""Read an XML document from a URI, and return a :mod:`lxml.etree`
	document."""
	return etree.parse(stream, parser=_get_xmlparser(), base_url=uri)

neuxml/neuxml/xmlmap/core.py

Lines 86 to 88 in 992ff81

	_loaded_schemas[uri] = etree.XMLSchema(
	etree.parse(uri, parser=_get_xmlparser(), base_url=base_uri)
	)

It looks like they aren't called by other functions themselves, so I think this should be safe? Could be worth checking if parse is called elsewhere and if etree.fromstring has the same problem.

Originally posted by @blms in #20 (comment)