docs/gst/gstreamer-sections.txt: made some defines private

docs/gst/gstreamer-sections.txt: made some defines private

Original commit message from CVS:
* docs/gst/gstreamer-sections.txt:
made some defines private
* docs/gst/tmpl/gstconfig.sgml:
* docs/gst/tmpl/gstqueue.sgml:
* docs/gst/tmpl/gsttaglist.sgml:
* docs/gst/tmpl/gsttypes.sgml:
* docs/gst/tmpl/gstutils.sgml:
* docs/pwg/appendix-porting.xml:
* gst/base/gstbasesink.h:
* gst/base/gstbasesrc.c:
* gst/base/gstbasesrc.h:
* gst/elements/gstfakesink.c: (gst_fake_sink_class_init):
* gst/elements/gstfakesrc.c: (gst_fake_src_class_init):
* gst/gstelement.c: (gst_element_class_init):
* gst/gstpad.c: (gst_pad_class_init):
* gst/gstqueue.c: (gst_queue_class_init):
* gst/gstxml.c: (gst_xml_class_init):
documented all undocumented signal inline
* libs/gst/controller/gst-controller.h:
added padding