Usage:
	sort -by phone <sample.xml | print

once sort and print are compiled.

These examples illustrate iter_tree, map_tree and find_element.


sort: 	reads an XML file from stdin, sorts the records, and prints the
 	result as XML.
delcol: reads an XML file from stdin, deletes a column from all records,
	and prints the result as XML.
print:	reads an XML file from stdin, and pretty-prints the file

The XML file must not contain a DTD. The programs assume the fixed DTD
record.dtd.