code: function(canvas, outfile, callback) {
      var fs = require("fs");
      var out = fs.createWriteStream(outfile);
      out.on("finish", function() {
          callback(true, out.bytesWritten);
      });
      var stream = canvas.createJPEGStream({
          bufsize: 2048,
          quality: 80
      });
      stream.on("error", function(err) {
          callback(false, err);
      });
      stream.on("data", function(buffer) {
          out.write(buffer);
      });
      stream.on("end", function() {
          out.end();
      });
  }
docs: Helper to write canvas to an output jpeg file
  Useful for writing manipulated image back to a file
  canvas - canvas to write out to disk
  outfile - string path to output file
  callback - function (result, data)
  result - boolean result true on successful write
  data - bytes written on success, or Error on failure