add --soft-target, --buf-delay

* add option to select video stream

chagne frontend mode, output a json dict, output to stdout by default, output duration with stats, not only once

So look for those, and concatenate the lines, so we don't strip the control
information from the first one only. Not sure if that's per spec, but I've
got one sample with those, and it's from the VLC test streams, so it must
be more than just an oddball.

 data which wasn't initialized when the init code was compiled out.

* use av_audio_resample_init
* new option to output information about files as json array

track audio and video eos separately so they are closer to each other if -s / -e is used to cut out segments

  if seeking between keyframes

  Only text (raw UTF-8 and SSA) is supported.
  SSA tags are not properly removed yet.
* update libkate to 0.3.1

use vstream.time_base if it those values are in range, use r_frame_rate otherwise, fixes issues with some mp4 files that list field and not frame rate in the later

- disable vhooks for now, not working with ffmpeg trunk
- store and use visble height/width before initializing decoder.
  this removes green borders for some flv vp6 files.