- Restructure plugin module using a "module struct" rather than global variables.

This include plugin module init and exit functions
  New type: clixon_plugin_t exposed via public API while struct clixon_plugin is private
- Makefile changes for static linkage using "LINKAGE=static"
- Moved nacm external init to later stage in backend_main

util/Makefile.in

@@ -105,6 +105,7 @@ $(top_srcdir)/lib/src/$(CLIXON_LIB):
 
 clean:
 	rm -f $(APPS) clixon_util_stream *.core
+	rm -f *.gcda *.gcno *.gcov # coverage
 
 # APPS
 clixon_util_xml: clixon_util_xml.c $(LIBDEPS)