rtpulpfecdec,enc: unbreak plugin gtk-doc build in autotools

rtpulpfecdec,enc: unbreak plugin gtk-doc build in autotools

Fix doc chunks to not use that syntax for links that have the
url as description, it will be put verbatim into the xml/*.xml
file and then the expat parser will throw a syntax error like:

  File "../../common/mangle-db.py", line 71, in <module>
    main()
  File "../../common/mangle-db.py", line 69, in main
    patch (details.replace("-details", ""), os.path.basename(details))
  File "../../common/mangle-db.py", line 20, in patch
    doc = xml.dom.minidom.parse(related)
  File "/usr/lib/python2.7/xml/dom/minidom.py", line 1918, in parse
    return expatbuilder.parse(file)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 924, in parse
    result = builder.parseFile(fp)
  File "/usr/lib/python2.7/xml/dom/expatbuilder.py", line 207, in parseFile
    parser.Parse(buffer, 0)
xml.parsers.expat.ExpatError: not well-formed (invalid token): line 84, column 7