ts: large rewrite of the TS muxer to produce better TS and support DVD

     subtitle.
     I have added some options:
        - bmin : minimum bitrate (bits/s) of the TS. Padding is added in
        case of insuffisant bitrate. (default: disabled).
        - bmax : maximum bitrate (bit/s) of the TS. It just drops packets
        to achieve the target. (default: disabled)
        - pcr : minimum delay between two pcr equal to dts of the video
        stream (default 100ms)
        - pcr-soft : minimum delay between two pcr interpolated from the
        pcr that are equal to dts. (default: none)
 Remarks:
  - bmin/bmax allow to create CBR stream.
  - Bitrate is calculated on a PCR time.
  - PCR delay cannot be less than length of a frame of the PCR stream.
  - PCR soft is used to help when using big PCR delay. It is usefull to
  produce stream with smoother bitrate variation.
  - Big PCR delay introduce more latency.

 TODO:
  Test stability, bugs ...