docs/plugins/: Added dvdec and dvdemux to docs.

docs/plugins/: Added dvdec and dvdemux to docs.

Original commit message from CVS:
* docs/plugins/Makefile.am:
* docs/plugins/gst-plugins-good-plugins-docs.sgml:
* docs/plugins/gst-plugins-good-plugins-sections.txt:
Added dvdec and dvdemux to docs.

* ext/dv/gstdvdec.c: (gst_dvdec_base_init), (gst_dvdec_chain):
Added docs.
Check frame sizes so we don't crash when don't have enough
data.
Send nice error messages on error.

* ext/dv/gstdvdemux.c: (gst_dvdemux_base_init),
(gst_dvdemux_class_init), (gst_dvdemux_init),
(gst_dvdemux_finalize), (gst_dvdemux_reset),
(gst_dvdemux_src_convert), (gst_dvdemux_sink_convert),
(gst_dvdemux_src_query), (gst_dvdemux_sink_query),
(gst_dvdemux_push_event), (gst_dvdemux_handle_sink_event),
(gst_dvdemux_convert_src_pair), (gst_dvdemux_convert_sink_pair),
(gst_dvdemux_convert_src_to_sink), (gst_dvdemux_handle_push_seek),
(gst_dvdemux_do_seek), (gst_dvdemux_handle_pull_seek),
(gst_dvdemux_handle_src_event), (gst_dvdemux_demux_audio),
(gst_dvdemux_demux_video), (gst_dvdemux_demux_frame),
(gst_dvdemux_flush), (gst_dvdemux_chain), (gst_dvdemux_loop),
(gst_dvdemux_sink_activate_push), (gst_dvdemux_sink_activate_pull),
(gst_dvdemux_sink_activate), (gst_dvdemux_change_state):
* ext/dv/gstdvdemux.h:
Added docs.
Implement pull mode.
Fix memleaks.
Reduce memcpy for the video demuxing.