Add Annodex elements from Alessendro Decina: skeleton and CMML.

Add Annodex elements from Alessendro Decina: skeleton and CMML.

Original commit message from CVS:
* configure.ac:
* docs/plugins/gst-plugins-good-plugins-sections.txt:
* ext/Makefile.am:
* ext/annodex/Makefile.am:
* ext/annodex/gstannodex.c:
* ext/annodex/gstannodex.h:
* ext/annodex/gstcmmldec.c:
* ext/annodex/gstcmmldec.h:
* ext/annodex/gstcmmlenc.c:
* ext/annodex/gstcmmlenc.h:
* ext/annodex/gstcmmlparser.c:
* ext/annodex/gstcmmlparser.h:
* ext/annodex/gstcmmltag.c:
* ext/annodex/gstcmmltag.h:
* ext/annodex/gstcmmlutils.c:
* ext/annodex/gstcmmlutils.h:
* ext/annodex/gstskeldec.c:
* ext/annodex/gstskeldec.h:
* ext/annodex/gstskeltag.c:
* ext/annodex/gstskeltag.h:
* tests/check/Makefile.am:
* tests/check/elements/cmmldec.c:
* tests/check/elements/cmmlenc.c:
* tests/check/elements/skeldec.c:
Add Annodex elements from Alessendro Decina: skeleton and CMML.
Includes tests & docs, oh my! Passes Thomas's -good checklist
entirely. Wow.