o Add support for requesting specific number of worker i/o threads;
o Add support for requesting specific number of worker i/o threads;

o provide explicit shutdown() method instead of requiring super-class
to figure out how to shutdown workers properly.

dsanders11/rtpproxy,synety-jdebp/rtpproxy,sippy/rtpproxy,jevonearth/rtpproxy,sippy/rtpproxy,sippy/rtpproxy,jevonearth/rtpproxy,dsanders11/rtpproxy,synety-jdebp/rtpproxy,synety-jdebp/rtpproxy,synety-jdebp/rtpproxy,dsanders11/rtpproxy,sippy/rtp_cluster,sippy/rtp_cluster,jevonearth/rtpproxy,jevonearth/rtpproxy