The ASF RTP spec demands that packets have their padding removed
and the padding size field set to 0 for packets when puting them
inside the RTP packets
Adds the brand new asfmux plugin, containing 3 elements:
asfmux, rtpasfpay and asfparse. This plugin was developed
as a GSoC 2009 project, with David Schleef as the mentor and
Thiago Santos as the student.