docs/plugins/: Add new docs. Scan c++ files too.

docs/plugins/: Add new docs. Scan c++ files too.

Original commit message from CVS:
* docs/plugins/Makefile.am:
* docs/plugins/gst-plugins-ugly-plugins-docs.sgml:
* docs/plugins/gst-plugins-ugly-plugins-sections.txt:
* docs/plugins/inspect/plugin-a52dec.xml:
* docs/plugins/inspect/plugin-amrnb.xml:
* docs/plugins/inspect/plugin-asf.xml:
* docs/plugins/inspect/plugin-dvdlpcmdec.xml:
* docs/plugins/inspect/plugin-dvdsub.xml:
* docs/plugins/inspect/plugin-iec958.xml:
* docs/plugins/inspect/plugin-lame.xml:
* docs/plugins/inspect/plugin-mad.xml:
* docs/plugins/inspect/plugin-mpeg2dec.xml:
* docs/plugins/inspect/plugin-mpegaudioparse.xml:
* docs/plugins/inspect/plugin-mpegstream.xml:
Add new docs. Scan c++ files too.
* ext/amrnb/amrnbdec.c: (gst_amrnbdec_base_init),
(gst_amrnbdec_event):
* ext/amrnb/amrnbenc.c: (gst_amrnbenc_base_init):
* ext/amrnb/amrnbparse.c: (gst_amrnbparse_base_init),
(gst_amrnbparse_loop):
Add documentation headers.
* ext/mad/gstmad.c:
* ext/mad/gstmad.h:
Refactor for docs.