Merge pull request #886 in FS/freeswitch from ~MGROOMS/freeswitch-matthew:bugfix/detect_audio_silence to master

* commit '6c3710df':
  FS-9264: Introduce two new api calls named detect_audio and detect_audio_silence. The existing wait_for_silence call never actually waits for silence until it first detects non-silence. There is also no way to set an independent timeout for detecting both the non-silence and then silence. This causes problems when wait_for_silence is called on an already quiet channel. Splitting the function up into two separate calls with separate timeouts offers more flexibility.