. complete commenting of modules_core.h and small modifications

 . complete commenting of modules_core.h and small modifications
 . separated MODULE_CONFIG_START and ADD_WINDOW (Henri, beware)
 . fixed a very, very old bug that caused namespace collision between
   plugins (Henri, beware: call your aout_getplugin function like this,
   not alsa_aout_getplugin)
 . removed the Debian specific clean rules from the Makefile, since they
   are already handled by the debian/rules script.
 . tidied a few compilation rules (-lfoo should always be at the end)