more docs inlined, splitted gstindex.{c,h}

more docs inlined, splitted gstindex.{c,h}

Original commit message from CVS:
* docs/gst/gstreamer-docs.sgml:
* docs/gst/gstreamer-sections.txt:
* docs/gst/tmpl/.cvsignore:
* gst/Makefile.am:
* gst/gst.h:
* gst/gstbin.c:
* gst/gstelement.h:
* gst/gstindex.c: (gst_index_class_init):
* gst/gstindex.h:
* gst/gstindexfactory.c: (gst_index_factory_get_type),
(gst_index_factory_class_init), (gst_index_factory_init),
(gst_index_factory_finalize), (gst_index_factory_new),
(gst_index_factory_destroy), (gst_index_factory_find),
(gst_index_factory_create), (gst_index_factory_make):
* gst/gstindexfactory.h:
* gst/gstpluginfeature.c:
* gst/gstpluginfeature.h:
* libs/gst/controller/gstcontroller.c: (gst_controller_new_valist):
more docs inlined, splitted gstindex.{c,h}