Starting on 'processxml' to beautify XML files

The new program 'processxml' is meant to rewrite and beautify
XML files created by 'scriptinterpreter'. Examples of such
beautifications include removal of empty tags or joining
timestep tags with short delays in between.
Only basic code is in place now, but none of the planned
features.

Rewriting Makefile to support both 'scriptinterpreter' and
'processxml'.