code: function BunyanFormatWritable (opts, out) {
    if (!(this instanceof BunyanFormatWritable)) return new BunyanFormatWritable(opts, out);
  
    opts = opts || {};
    opts.objectMode = true;
    Writable.call(this, opts);
  
    this.opts = xtend({ 
      outputMode: 'short', 
      color: true,
      colorFromLevel: {
        10: 'brightBlack',    // TRACE
        20: 'brightBlack',    // DEBUG
        30: 'green',          // INFO
        40: 'magenta',        // WARN
        50: 'red',            // ERROR
        60: 'brightRed',      // FATAL
      }
    }, opts);
    this.out = out || process.stdout;
  }
docs: Creates a writable stream that formats bunyan records written to it.
  
  @name BunyanFormatWritable
  @function
  @param opts {Options} passed to bunyan format function
  - outputMode: short|long|simple|json|bunyan
  - color (true): toggles colors in output
  - colorFromLevel: allows overriding log level colors
  @param out {Stream} (process.stdout) writable stream to write
  @return {WritableStream} that you can pipe bunyan output into