include/Makefile.am: install new headers,
     * include/hpp/core/freeflyer-joint.hh: remove trailing white spaces,
     * include/hpp/core/parser.hh, add callback functions
     * include/hpp/core/rotation-joint.hh: new,
     * include/hpp/core/translation-joint.hh, new,
     * src/parser.cc: implement new callback functions