def initialize(options)
        @yield_block = options.fetch(:yield, nil)
        @stdout      = options.fetch(:stdout, $stdout)
        @stderr      = options.fetch(:stderr, $stderr)
      end
Options:
* (optional) :yield - a block to call when the inmate yields
* (optional) :stdout - an IO for writing STDOUT from the inmate
* (optional) :stderr - an IO for writing STDERR from the inmate