_getMessage should be inlined and/or renamed #32

I think _getMessage should be:

• Inlined as we are using it on only one place. I would assign the one line to a variable and pass it to this._iosDeviceLibStdioHandler.writeData
• Named something like _serializeNativeMethodCall... something that will ring the right bell when you read it.
  https://github.com/telerik/ios-device-lib/blob/382c9c63dd1999ef247def16a3787b5987d63649/index.js#L126