Add preliminary FLV/RTMP output (incomplete)

- obs-outputs module:  Add preliminary code to send out data, and add
   an FLV muxer.  This time we don't really need to build the packets
   ourselves, we can just use the FLV muxer and send it directly to
   RTMP_Write and it should automatically parse the entire stream for us
   without us having to do much manual code at all.  We'll see how it
   goes.

 - libobs:  Add AVC NAL packet parsing code

 - libobs/media-io:  Add quick helper functions for audio/video to get
   the width/height/fps/samplerate/etc rather than having to query the
   info structures each time.

 - libobs (obs-output.c):  Change 'connect' signal to 'start' and 'stop'
   signals.  'start' now specifies an error code rather than whether it
   simply failed, that way the client can actually know *why* a failure
   occurred.  Added those error codes to obs-defs.h.

 - libobs:  Add a few functions to duplicate/free encoder packets

libobs/media-io/audio-io.h

@@ -185,12 +185,14 @@ EXPORT bool audio_output_active(audio_t audio);
 EXPORT size_t audio_output_blocksize(audio_t audio);
 EXPORT size_t audio_output_planes(audio_t audio);
 EXPORT size_t audio_output_channels(audio_t audio);
+EXPORT uint32_t audio_output_samplerate(audio_t audio);
 EXPORT const struct audio_output_info *audio_output_getinfo(audio_t audio);
 
 EXPORT audio_line_t audio_output_createline(audio_t audio, const char *name);
 EXPORT void audio_line_destroy(audio_line_t line);
 EXPORT void audio_line_output(audio_line_t line, const struct audio_data *data);
 
+
 #ifdef __cplusplus
 }
 #endif