Fixing use of CFLAGS and LDFLAGS

Fixing use of CFLAGS and LDFLAGS for 'scriptinterpreter' and
'processxml'.
Also, migrating used XML library from 'expat' to 'libxml2'.
Refactoring from 'expat' to 'libxml2'

Refactoring processxml from 'expat' to 'libxml2' to take
advantage of a in-memory tree representation of the XML file
instead of a stream-based parser like expat.