docs/plugins/: Added smoke and jpeg to the docs.

docs/plugins/: Added smoke and jpeg to the 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:
* docs/plugins/gst-plugins-good-plugins.hierarchy:
Added smoke and jpeg to the docs.
* ext/jpeg/Makefile.am:
* ext/jpeg/gstjpeg.c: (plugin_init):
* ext/jpeg/gstjpegdec.c: (gst_jpeg_dec_chain):
* ext/jpeg/gstjpegenc.h:
* ext/jpeg/gstsmokedec.c: (gst_smokedec_init),
(gst_smokedec_chain):
* ext/jpeg/gstsmokedec.h:
* ext/jpeg/gstsmokeenc.c: (gst_smokeenc_chain):
* ext/jpeg/gstsmokeenc.h:
* ext/jpeg/smokecodec.h:
Port smokedec (fixes #331905).
Added some docs.
Some cleanups.