Adding documentation for videomixer on my way with a funny sample pipeline.

Adding documentation for videomixer on my way with a funny sample pipeline.

Original commit message from CVS:
2005-12-12  Julien MOUTTE  <julien@moutte.net>

* docs/plugins/Makefile.am:
* docs/plugins/gst-plugins-good-plugins-docs.sgml:
* docs/plugins/gst-plugins-good-plugins-sections.txt:
* docs/plugins/gst-plugins-good-plugins.hierarchy:
* gst/videomixer/videomixer.c:
(gst_videomixer_pad_sink_setcaps),
(gst_videomixer_getcaps), (gst_videomixer_fill_queues),
(gst_videomixer_update_queues), (gst_videomixer_collected):
Adding
documentation for videomixer on my way with a funny sample
pipeline.