For the new parser, there is a debug function called print_tree. This
was originally calling the print_tree_i function which was recursively
walking the parse tree and printing out the tree structs type and
value. I've changed print_tree to call a new function called
print_tree_xml which will do the same but output xml. When running
Csound, this outputs the xml in the midst of all the other output to
screen so one would need to capture the output to file, then cut out
the XML for the parse tree.
I did this change so that I could take the generated XML and save it
into a file and then view the XML within Firefox which makes it easy
to collapse the nodes and to read through the structure of the parse
tree while debugging.
I'm pretty sure that this change should be more useful all around but
have left the other print_tree_i in the source file in case we decide
to use it later.